Terrain tree from 2 crossed sprites/quads

Hi,
I’m want to create terrain tree from 2 crossed sprites/quads.
83069-s1.png

But when I’m trying to use this object/prefab as Terrain tree, getting this message:
The tree GameObject 1 couldn’t be instanced because the prefab contains no valid mesh renderer.
UnityEditor.HostView:OnGUI()

So 2 child GO have meshes, but Parent don’t contain them?
How can I combine child objects meshes to use complete/parent GO as Terrain tree?

Have you found something? I saw I guy do it on youtube: Got sprite tress working as unity trees - YouTube