diff --git a/tests/materializer/unions/test_mixed_discrimination.py b/tests/materializer/unions/test_callable_string_mixed_discrimination.py
similarity index 94%
rename from tests/materializer/unions/test_mixed_discrimination.py
rename to tests/materializer/unions/test_callable_string_mixed_discrimination.py
index 60f34a7..d4bbf97 100644
--- a/tests/materializer/unions/test_mixed_discrimination.py
+++ b/tests/materializer/unions/test_callable_string_mixed_discrimination.py
@@ -1,4 +1,4 @@
-"""Tests for mixed string/callable discriminated unions.
+"""Tests for mixed callable/string discriminated unions with a simple model union member.
 
 Covers:
 - Callable discriminated union where one tag point to simple model
@@ -116,7 +116,7 @@ class NestedGroupedThing(BaseModel):
 
 
 @pytest.mark.parametrize("param", params)
-def test_mixed_discriminated_union(param):
+def test_callable_string_mixed_discrimination(param):
     materializer = ModelMaterializer(**param.kwargs)
     assert list(materializer.generate_bindings()) == param.expected.bindings
     assert [
@@ -124,7 +124,7 @@ def test_mixed_discriminated_union(param):
     ] == param.expected.model_dump
 
 
-def test_mixed_discriminated_union_model_types():
+def test_callable_string_mixed_discrimination_model_types():
     cat, dog, car = ModelMaterializer(model=Model, data=data).generate_models()
     assert isinstance(cat.thing, Cat)
     assert isinstance(dog.thing, Dog)
diff --git a/tests/materializer/unions/test_string_callable_mixed_discrimination.py b/tests/materializer/unions/test_string_callable_mixed_discrimination.py
new file mode 100644
index 0000000..a284353
--- /dev/null
+++ b/tests/materializer/unions/test_string_callable_mixed_discrimination.py
@@ -0,0 +1,188 @@
+"""Tests for mixed string/callable discriminated unions with a simple model union member.
+
+Covers:
+- String discriminated union where one member is a simple model
+  and another points to a nested callable discriminated union.
+  This is the inverse test to test_callable_string_mixed_discrimination.py.
+- Discrimnated union model aggregation (top-level + nested union aggregation)
+"""
+
+from typing import Annotated, Any, Literal
+
+import pytest
+from graphty import ConfigDict, ModelMaterializer
+from pydantic import BaseModel, Discriminator, Field, Tag
+from tests.materializer.param import Expected, Parameter
+
+
+class Cat(BaseModel):
+    kind: Literal["cat"]
+    name: str
+
+
+class RoadBike(BaseModel):
+    kind: Literal["bike"]
+    bike_type: Literal["road"]
+
+
+class MountainBike(BaseModel):
+    kind: Literal["bike"]
+    bike_type: Literal["mountain"]
+
+
+def get_bike_type(v: Any) -> str | None:
+    bike_type = (
+        v.get("bike_type") if isinstance(v, dict) else getattr(v, "bike_type", None)
+    )
+    if bike_type == "road":
+        return "road"
+    if bike_type == "mountain":
+        return "mountain"
+
+
+Bike = Annotated[
+    Annotated[RoadBike, Tag("road")] | Annotated[MountainBike, Tag("mountain")],
+    Discriminator(get_bike_type),
+]
+
+Thing = Annotated[Bike | Cat, Field(discriminator="kind")]
+
+
+class Model(BaseModel):
+    thing: Thing
+
+
+class GroupedThing(BaseModel):
+    model_config = ConfigDict(group_by="kind")
+
+    kind: str
+    nested: list[Thing]
+
+
+class NestedGroupedThing(BaseModel):
+    model_config = ConfigDict(group_by="kind")
+
+    kind: str
+    nested: list[GroupedThing]
+
+
+data = [
+    {"kind": "cat", "name": "Muzi", "bike_type": None},
+    {"kind": "bike", "name": None, "bike_type": "road"},
+    {"kind": "bike", "name": None, "bike_type": "mountain"},
+]
+
+
+params = [
+    Parameter(
+        kwargs={"model": Model, "data": data},
+        expected=Expected(
+            bindings=[
+                {"thing": {"kind": "cat", "bike_type": None, "name": "Muzi"}},
+                {"thing": {"kind": "bike", "bike_type": "road", "name": None}},
+                {"thing": {"kind": "bike", "bike_type": "mountain", "name": None}},
+            ],
+            model_dump=[
+                {"thing": {"kind": "cat", "name": "Muzi"}},
+                {"thing": {"kind": "bike", "bike_type": "road"}},
+                {"thing": {"kind": "bike", "bike_type": "mountain"}},
+            ],
+        ),
+    ),
+    Parameter(
+        kwargs={"model": GroupedThing, "data": data},
+        expected=Expected(
+            bindings=[
+                {
+                    "kind": "cat",
+                    "nested": [{"kind": "cat", "bike_type": None, "name": "Muzi"}],
+                },
+                {
+                    "kind": "bike",
+                    "nested": [
+                        {"kind": "bike", "bike_type": "road", "name": None},
+                        {"kind": "bike", "bike_type": "mountain", "name": None},
+                    ],
+                },
+            ],
+            model_dump=[
+                {"kind": "cat", "nested": [{"kind": "cat", "name": "Muzi"}]},
+                {
+                    "kind": "bike",
+                    "nested": [
+                        {"kind": "bike", "bike_type": "road"},
+                        {"kind": "bike", "bike_type": "mountain"},
+                    ],
+                },
+            ],
+        ),
+    ),
+    Parameter(
+        kwargs={"model": NestedGroupedThing, "data": data},
+        expected=Expected(
+            bindings=[
+                {
+                    "kind": "cat",
+                    "nested": [
+                        {
+                            "kind": "cat",
+                            "nested": [
+                                {"kind": "cat", "bike_type": None, "name": "Muzi"}
+                            ],
+                        }
+                    ],
+                },
+                {
+                    "kind": "bike",
+                    "nested": [
+                        {
+                            "kind": "bike",
+                            "nested": [
+                                {"kind": "bike", "bike_type": "road", "name": None},
+                                {"kind": "bike", "bike_type": "mountain", "name": None},
+                            ],
+                        }
+                    ],
+                },
+            ],
+            model_dump=[
+                {
+                    "kind": "cat",
+                    "nested": [
+                        {"kind": "cat", "nested": [{"kind": "cat", "name": "Muzi"}]}
+                    ],
+                },
+                {
+                    "kind": "bike",
+                    "nested": [
+                        {
+                            "kind": "bike",
+                            "nested": [
+                                {"kind": "bike", "bike_type": "road"},
+                                {"kind": "bike", "bike_type": "mountain"},
+                            ],
+                        }
+                    ],
+                },
+            ],
+        ),
+    ),
+]
+
+
+@pytest.mark.parametrize("param", params)
+def test_string_callable_mixed_discrimination(param):
+    materializer = ModelMaterializer(**param.kwargs)
+    assert list(materializer.generate_bindings()) == param.expected.bindings
+    assert [
+        m.model_dump() for m in materializer.generate_models()
+    ] == param.expected.model_dump
+
+
+def test_string_callable_mixed_discrimination_model_types():
+    cat, road_bike, mountain_bike = ModelMaterializer(
+        model=Model, data=data
+    ).generate_models()
+    assert isinstance(cat.thing, Cat)
+    assert isinstance(road_bike.thing, RoadBike)
+    assert isinstance(mountain_bike.thing, MountainBike)