Slams head into desk. Always thought the main mesh (_tree) had to be a single mesh. Hence you couldnt have more than 1 material as prefab doesn't do face materials.
The _tree can be several meshes so you can do several materials. eg cube made of 6 planes and 6 materials. Oh well, learnt something new. I'll try not to think about how many hours spent on mapping UVs to a single material :( ps thanks
