Terrain only renders the mesh renderer in root gameObject of a tree prefab

To reproduce:
1. Open attached project
2. Open SampleScene

Expected Result: All the Mesh Renderers found in a tree prefab are visible (in this scene, you should see many trees)
Actual result: Only the mesh renderer in the root of the prefab is visible (in this scene, you will only see small barrel meshes visible, as they are in the root of the prefab)

Note: The trees on the terrain are a prefab, of which root object is a barrel, it has child objects with tree part mesh renderers.
Alternatively, if the fix is not possible, there should be a warning in the Terrain system about using prefabs with a hierarchy of mesh renderers as Trees.

Reproduced on: 2017.4.20f2, 2019.2.0a11