Importing custom tree into terrain editor - how do I do it?

So I downloaded this awesome custom tree pack, but I'm not sure how to get it into the terrain editor. I tried following the instructions on the wiki, but they don't work very well.

When I drag one of the models into my scene to look at how its structured, whoever made the trees has the trunk and branches sections of the tree set as two child objects of the model, and then I have to drag the appropriate materials (that came with the pack) to those child objects.

The U3D documentation mentions that the branches and bark have to be materials attached to the tree, not child objects of the tree. How do I achieve this?

if you get only tree model, you can export your tree to be one FBX file in one folder and put the folder into "Ambient-Occlusion" folder. select the fbx file in your project and you can find deffuse shade by default on inspector. just change it to be Nature/Soft Occlusion Leaves and Nature/Soft Occlusion Bark shader.

If you get unity package of tree, just import it into your project.