diff --git a/setup.py b/setup.py
index 1fef10d..9ccd3d8 100644
--- a/setup.py
+++ b/setup.py
@@ -41,7 +41,8 @@
         },
         entry_points={
             "ansys.tools.protoc_helper.proto_provider": [
-                "ansys.api.acp.v0=ansys.api.acp.v0"
+                "ansys.api.acp.v0=ansys.api.acp.v0",
+                "ansys.api.acp.internal=ansys.api.acp.internal",
             ],
         },
         cmdclass=CMDCLASS_OVERRIDE,
diff --git a/src/ansys/api/acp/internal/tree.proto b/src/ansys/api/acp/internal/tree.proto
new file mode 100644
index 0000000..9151960
--- /dev/null
+++ b/src/ansys/api/acp/internal/tree.proto
@@ -0,0 +1,52 @@
+// Copyright (C) 2022 - 2025 ANSYS, Inc. and/or its affiliates.
+// SPDX-License-Identifier: MIT
+//
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+syntax = "proto3";
+package ansys.api.acp.internal.tree;
+
+// The package name 'internal' has special meaning in Go:
+// other modules cannot import it.
+// To avoid this, we use 'unstable' instead of 'internal'.
+// This only affects the generated Go code.
+option go_package = "github.com/ansys/ansys-api-acp/ansys/api/acp/unstable/tree";
+
+// This is an internal proto definition and should not be
+// used in any public interface.
+// Stability and backwards compatibility is not guaranteed.
+
+import "ansys/api/acp/v0/base.proto";
+
+message TreeObject {
+    ansys.api.acp.v0.base.BasicInfo basic_info = 1;
+    ansys.api.acp.v0.base.ResourcePath leaf_resource_path = 2;
+}
+
+message ListTreeObjectsRequest {
+    // The resource path must represent a model
+    ansys.api.acp.v0.base.ResourcePath resource_path = 1;
+}
+
+message FlatTree { repeated TreeObject tree_objects = 1; }
+
+service TreeObjectService {
+    rpc ListTreeObjects(ListTreeObjectsRequest) returns (FlatTree);
+}