diff --git a/graphify/tree_html.py b/graphify/tree_html.py
index 65d151cde..c0a44b9ff 100644
--- a/graphify/tree_html.py
+++ b/graphify/tree_html.py
@@ -152,18 +152,27 @@ def _attach_files(
     return root_node, matched_files, by_file
 
 
+_NO_REPO_LABEL = "(no repo)"
+
+
 def _repo_groups(
     file_nodes: List[Dict[str, Any]],
-) -> Dict[str, List[Dict[str, Any]]]:
-    """Group nodes by their ``repo`` tag (set by ``merge-graphs`` / ``global add``).
+) -> "tuple[Dict[str, List[Dict[str, Any]]], List[Dict[str, Any]]]":
+    """Split nodes into ``({repo tag: nodes}, untagged nodes)``.
 
-    Nodes without a usable tag go under ``"(no repo)"`` so they are not lost.
+    The tag is the ``repo`` attribute set by ``merge-graphs`` / ``global add``.
+    Untagged nodes are returned separately so they never count as a repo: only
+    real tags decide whether a graph is treated as a merged one.
     """
     groups: Dict[str, List[Dict[str, Any]]] = defaultdict(list)
+    untagged: List[Dict[str, Any]] = []
     for n in file_nodes:
         tag = n.get("repo")
-        groups[tag if isinstance(tag, str) and tag else "(no repo)"].append(n)
-    return groups
+        if isinstance(tag, str) and tag:
+            groups[tag].append(n)
+        else:
+            untagged.append(n)
+    return groups, untagged
 
 
 def build_tree(
@@ -195,9 +204,11 @@ def build_tree(
         return {"name": "(empty graph)", "total_count": 0, "children": []}
 
     explicit_root = root is not None
-    groups = _repo_groups(file_nodes)
+    groups, untagged = _repo_groups(file_nodes)
 
     if len(groups) < 2:
+        # Zero or one real repo tag: not a merged graph. Every node, tagged or
+        # not, goes through the original single-root path.
         if root is None:
             root = _common_root([n["source_file"] for n in file_nodes])
         root_node, matched_files, by_file = _attach_files(
@@ -214,8 +225,11 @@ def build_tree(
         }
         total_matched = total_files = 0
         sample = ""
-        for tag in sorted(groups):
-            group = groups[tag]
+        ordered = sorted(groups.items())
+        if untagged:
+            # Kept visible, but only once two real tags made this a merged graph.
+            ordered.append((_NO_REPO_LABEL, untagged))
+        for tag, group in ordered:
             paths = [n["source_file"] for n in group]
             if root is not None:
                 group_root = root
diff --git a/tests/test_tree_html.py b/tests/test_tree_html.py
index 697b79cdb..72b62156e 100644
--- a/tests/test_tree_html.py
+++ b/tests/test_tree_html.py
@@ -136,6 +136,26 @@ def test_build_tree_merged_graph_untagged_nodes_are_kept():
     assert set(_by_name(build_tree(graph))) == {"repo-a", "repo-b", "(no repo)"}
 
 
+def test_build_tree_partially_tagged_single_repo_is_not_a_merged_graph():
+    """One real repo tag plus untagged nodes is not a merged graph: it must
+    take the original single-root path, not grow a "(no repo)" sibling."""
+    graph = {"nodes": [
+        {"id": "a", "label": "A", "source_file": "pkg/a.py", "repo": "only-repo"},
+        {"id": "b", "label": "B", "source_file": "pkg/b.py"},
+    ]}
+    tree = build_tree(graph)
+    assert tree["name"] == "pkg"
+    assert set(_by_name(tree)) == {"a.py", "b.py"}
+
+
+def test_build_tree_untagged_graph_is_unchanged_by_repo_grouping():
+    graph = _graph({"pkg/a.py": "func_a", "pkg/sub/b.py": "func_b"})
+    assert "repo" not in graph["nodes"][0]
+    tree = build_tree(graph)
+    assert tree["name"] == "pkg"
+    assert {"a.py", "sub"} <= set(_by_name(tree))
+
+
 def test_build_tree_merged_graph_explicit_root_matching_nothing_raises():
     graph = _merged_graph({
         "repo-a": {"src/a.py": "A"},