Unity 5 Custom Imported Trees

Hey I am having trouble making my trees generate with the terrain tree painter. I made the trees in Maya and I made a prefab in unity 5 with the soft occlusion shaders for the leaves and the bark. When I place the tree prefab into the terrain tree painter it wont show up on the terrain when I paint the tree on the terrain. Does anyone know how to paint custom trees onto the terrain? I can not find any tutorials or explainations on the web or Youtube. Thanks