diff --git a/src/python/qubed/Qube.py b/src/python/qubed/Qube.py
index 224eb0d..b9fb503 100644
--- a/src/python/qubed/Qube.py
+++ b/src/python/qubed/Qube.py
@@ -49,9 +49,15 @@ class Qube:
     def metadata(self):
         return self.data.metadata
 
+    @property
+    def dtype(self):
+        return self.data.dtype
+
     def replace(self, **kwargs) -> Qube:
         data_keys = {
-            k: v for k, v in kwargs.items() if k in ["key", "values", "metadata"]
+            k: v
+            for k, v in kwargs.items()
+            if k in ["key", "values", "metadata", "dtype"]
         }
         node_keys = {k: v for k, v in kwargs.items() if k == "children"}
         if not data_keys and not node_keys:
@@ -69,7 +75,9 @@ class Qube:
     @classmethod
     def make(cls, key: str, values: ValueGroup, children, **kwargs) -> Qube:
         return cls(
-            data=NodeData(key, values, metadata=kwargs.get("metadata", frozendict())),
+            data=NodeData(
+                key, values, metadata=frozendict(kwargs.get("metadata", frozendict()))
+            ),
             children=tuple(sorted(children, key=lambda n: ((n.key, n.values.min())))),
         )
 
@@ -217,11 +225,17 @@ class Qube:
             if name is not None
             else self
         )
-        return "".join(node_tree_to_string(node=node, depth=depth))
+        out = "".join(node_tree_to_string(node=node, depth=depth))
+        if out[-1] == "\n":
+            out = out[:-1]
+        return out
 
     def __str__(self):
         return self.__str_helper__()
 
+    def __repr__(self):
+        return f"Qube({self.__str_helper__()})"
+
     def print(self, depth=None, name: str | None = None):
         print(self.__str_helper__(depth=depth, name=name))
 
@@ -409,7 +423,8 @@ class Qube:
         def convert(node: Qube) -> Qube:
             if node.key in converters:
                 converter = converters[node.key]
-                new_node = node.replace(values=QEnum(map(converter, node.values)))
+                values = [converter(v) for v in node.values]
+                new_node = node.replace(values=QEnum(values), dtype=type(values[0]))
                 return new_node
             return node
 
diff --git a/src/python/qubed/metadata.py b/src/python/qubed/metadata.py
index 1436178..db460d5 100644
--- a/src/python/qubed/metadata.py
+++ b/src/python/qubed/metadata.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from typing import TYPE_CHECKING, Iterator
 
 import numpy as np
@@ -13,7 +15,7 @@ def make_node(
     key: str,
     values: Iterator,
     shape: list[int],
-    children: "tuple[Qube]",
+    children: tuple[Qube, ...],
     metadata: dict[str, np.ndarray] | None = None,
 ):
     return cls.make(
@@ -30,11 +32,11 @@ def from_nodes(cls, nodes, add_root=True):
     shape = [len(n["values"]) for n in nodes.values()]
     nodes = nodes.items()
     *nodes, (key, info) = nodes
-    root = make_node(shape=shape, children=(), key=key, **info)
+    root = make_node(cls, shape=shape, children=(), key=key, **info)
 
     for key, info in reversed(nodes):
         shape.pop()
-        root = make_node(shape=shape, children=(root,), key=key, **info)
+        root = make_node(cls, shape=shape, children=(root,), key=key, **info)
 
     if add_root:
         return cls.root_node(children=(root,))
diff --git a/src/python/qubed/node_types.py b/src/python/qubed/node_types.py
index 433198f..563d813 100644
--- a/src/python/qubed/node_types.py
+++ b/src/python/qubed/node_types.py
@@ -13,6 +13,7 @@ class NodeData:
     metadata: frozendict[str, np.ndarray] = field(
         default_factory=lambda: frozendict({}), compare=False
     )
+    dtype: type = str
 
     def summary(self) -> str:
         return f"{self.key}={self.values.summary()}" if self.key != "root" else "root"
diff --git a/src/python/qubed/set_operations.py b/src/python/qubed/set_operations.py
index 63f9797..037b952 100644
--- a/src/python/qubed/set_operations.py
+++ b/src/python/qubed/set_operations.py
@@ -40,7 +40,6 @@ def QEnum_intersection(
 
     for index_a, val_A in enumerate(A.values):
         if val_A in B.values:
-            # print(f"{val_A} in both")
             just_B.pop(val_A)
             intersection[val_A] = (
                 index_a  # We throw away any overlapping metadata from B
@@ -116,9 +115,8 @@ def operation(A: Qube, B: Qube, operation_type: SetOperation, node_type) -> Qube
 
     # For every node group, perform the set operation
     for key, (A_nodes, B_nodes) in nodes_by_key.items():
-        new_children.extend(
-            _operation(key, A_nodes, B_nodes, operation_type, node_type)
-        )
+        output = list(_operation(key, A_nodes, B_nodes, operation_type, node_type))
+        new_children.extend(output)
 
     # Whenever we modify children we should recompress them
     # But since `operation` is already recursive, we only need to compress this level not all levels
@@ -193,17 +191,17 @@ def compress_children(children: Iterable[Qube]) -> tuple[Qube, ...]:
     """
     # Take the set of new children and see if any have identical key, metadata and children
     # the values may different and will be collapsed into a single node
-    identical_children = defaultdict(set)
+
+    identical_children = defaultdict(list)
     for child in children:
         # only care about the key and children of each node, ignore values
         h = hash((child.key, tuple((cc.structural_hash for cc in child.children))))
-        identical_children[h].add(child)
+        identical_children[h].append(child)
 
     # Now go through and create new compressed nodes for any groups that need collapsing
     new_children = []
-    for child_set in identical_children.values():
-        if len(child_set) > 1:
-            child_list = list(child_set)
+    for child_list in identical_children.values():
+        if len(child_list) > 1:
             example = child_list[0]
             node_type = type(example)
             key = child_list[0].key
@@ -217,9 +215,10 @@ def compress_children(children: Iterable[Qube]) -> tuple[Qube, ...]:
                 k: [child.metadata[k] for child in child_list]
                 for k in example.metadata.keys()
             }
+
             metadata: frozendict[str, np.ndarray] = frozendict(
                 {
-                    k: np.concatenate(metadata_group, axis=-1)
+                    k: np.concatenate(metadata_group, axis=0)
                     for k, metadata_group in metadata_groups.items()
                 }
             )
@@ -227,12 +226,14 @@ def compress_children(children: Iterable[Qube]) -> tuple[Qube, ...]:
             node_data = NodeData(
                 key=key,
                 metadata=metadata,
-                values=QEnum((v for child in child_list for v in child.data.values)),
+                values=QEnum(set(v for child in child_list for v in child.data.values)),
             )
-            new_child = node_type(data=node_data, children=child_list[0].children)
+            children = [cc for c in child_list for cc in c.children]
+            compressed_children = compress_children(children)
+            new_child = node_type(data=node_data, children=compressed_children)
         else:
             # If the group is size one just keep it
-            new_child = child_set.pop()
+            new_child = child_list.pop()
 
         new_children.append(new_child)
 
diff --git a/src/python/qubed/tree_formatters.py b/src/python/qubed/tree_formatters.py
index 7c83af8..49ead5a 100644
--- a/src/python/qubed/tree_formatters.py
+++ b/src/python/qubed/tree_formatters.py
@@ -4,6 +4,8 @@ import random
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Iterable
 
+import numpy as np
+
 if TYPE_CHECKING:
     from .Qube import Qube
 
@@ -68,17 +70,51 @@ def node_tree_to_string(node: Qube, prefix: str = "", depth=None) -> Iterable[st
         )
 
 
+def summarize_node_html(
+    node: Qube, collapse=False, max_summary_length=50, **kwargs
+) -> tuple[str, Qube]:
+    """
+    Extracts a summarized representation of the node while collapsing single-child paths.
+    Returns the summary string and the last node in the chain that has multiple children.
+    """
+    summaries = []
+
+    while True:
+        path = node.summary(**kwargs)
+        summary = path
+        if "is_leaf" in node.metadata and node.metadata["is_leaf"]:
+            summary += " 🌿"
+
+        if len(summary) > max_summary_length:
+            summary = summary[:max_summary_length] + "..."
+        info = (
+            f"dtype: {node.dtype.__name__}\n"
+            f"metadata: {dict((k, np.shape(v)) for k, v in node.metadata.items())}\n"
+        )
+        summary = f'<span class="qubed-node" data-path="{path}" title="{info}">{summary}</span>'
+        summaries.append(summary)
+        if not collapse:
+            break
+
+        # Move down if there's exactly one child, otherwise stop
+        if len(node.children) != 1:
+            break
+        node = node.children[0]
+
+    return ", ".join(summaries), node
+
+
 def _node_tree_to_html(
     node: Qube, prefix: str = "", depth=1, connector="", **kwargs
 ) -> Iterable[str]:
-    summary, path, node = summarize_node(node, **kwargs)
+    summary, node = summarize_node_html(node, **kwargs)
 
     if len(node.children) == 0:
-        yield f'<span class="qubed-node leaf" data-path="{path}">{connector}{summary}</span>'
+        yield f'<span class="qubed-level">{connector}{summary}</span>'
         return
     else:
         open = "open" if depth > 0 else ""
-        yield f'<details {open} data-path="{path}"><summary class="qubed-node">{connector}{summary}</summary>'
+        yield f'<details {open}><summary class="qubed-level">{connector}{summary}</summary>'
 
     for index, child in enumerate(node.children):
         connector = "└── " if index == len(node.children) - 1 else "├── "
@@ -114,7 +150,7 @@ def node_tree_to_html(
                 margin-left: 0;
             }
 
-            .qubed-node a {
+            .qubed-level a {
                 margin-left: 10px;
                 text-decoration: none;
             }
@@ -128,7 +164,7 @@ def node_tree_to_html(
                 display: block;
             }
 
-            summary:hover,span.leaf:hover {
+            span.qubed-node:hover {
                 background-color: #f0f0f0;
             }
 
@@ -140,7 +176,7 @@ def node_tree_to_html(
                 content: " ▼";
             }
 
-            .leaf {
+            .qubed-level {
                 text-overflow: ellipsis;
                 overflow: hidden;
                 text-wrap: nowrap;
diff --git a/tests/test_formatters.py b/tests/test_formatters.py
index 5eb8685..7278927 100644
--- a/tests/test_formatters.py
+++ b/tests/test_formatters.py
@@ -21,7 +21,7 @@ root
 """.strip()
 
 as_html = """
-<details open data-path="root"><summary class="qubed-node">root</summary><span class="qubed-node leaf" data-path="class=od,expver=0001/0002,param=1/2">├── class=od, expver=0001/0002, param=1/2</span><details open data-path="class=rd"><summary class="qubed-node">└── class=rd</summary><span class="qubed-node leaf" data-path="expver=0001,param=1/2/3">    ├── expver=0001, param=1/2/3</span><span class="qubed-node leaf" data-path="expver=0002,param=1/2">    └── expver=0002, param=1/2</span></details></details>
+<details open><summary class="qubed-level"><span class="qubed-node" data-path="root" title="dtype: str\nmetadata: {}\n">root</span></summary><span class="qubed-level">├── <span class="qubed-node" data-path="class=od" title="dtype: str\nmetadata: {}\n">class=od</span>, <span class="qubed-node" data-path="expver=0001/0002" title="dtype: str\nmetadata: {}\n">expver=0001/0002</span>, <span class="qubed-node" data-path="param=1/2" title="dtype: str\nmetadata: {}\n">param=1/2</span></span><details open><summary class="qubed-level">└── <span class="qubed-node" data-path="class=rd" title="dtype: str\nmetadata: {}\n">class=rd</span></summary><span class="qubed-level">    ├── <span class="qubed-node" data-path="expver=0001" title="dtype: str\nmetadata: {}\n">expver=0001</span>, <span class="qubed-node" data-path="param=1/2/3" title="dtype: str\nmetadata: {}\n">param=1/2/3</span></span><span class="qubed-level">    └── <span class="qubed-node" data-path="expver=0002" title="dtype: str\nmetadata: {}\n">expver=0002</span>, <span class="qubed-node" data-path="param=1/2" title="dtype: str\nmetadata: {}\n">param=1/2</span></span></details></details>
 """.strip()
 
 
diff --git a/tests/test_metadata.py b/tests/test_metadata.py
index e69de29..6d9e416 100644
--- a/tests/test_metadata.py
+++ b/tests/test_metadata.py
@@ -0,0 +1,45 @@
+from frozendict import frozendict
+from qubed import Qube
+
+
+def make_set(entries):
+    return set((frozendict(a), frozendict(b)) for a, b in entries)
+
+
+def test_simple_union():
+    q = Qube.from_nodes(
+        {
+            "class": dict(values=["od", "rd"]),
+            "expver": dict(values=[1, 2]),
+            "stream": dict(
+                values=["a", "b", "c"], metadata=dict(number=list(range(12)))
+            ),
+        }
+    )
+
+    r = Qube.from_nodes(
+        {
+            "class": dict(values=["xd"]),
+            "expver": dict(values=[1, 2]),
+            "stream": dict(
+                values=["a", "b", "c"], metadata=dict(number=list(range(12, 18)))
+            ),
+        }
+    )
+
+    expected_union = Qube.from_nodes(
+        {
+            "class": dict(values=["od", "rd", "xd"]),
+            "expver": dict(values=[1, 2]),
+            "stream": dict(
+                values=["a", "b", "c"], metadata=dict(number=list(range(18)))
+            ),
+        }
+    )
+
+    union = q | r
+
+    assert union == expected_union
+    assert make_set(expected_union.leaves_with_metadata()) == make_set(
+        union.leaves_with_metadata()
+    )