I made this scene in blender and imported it in unity5. Here You can see the tree is missing faces in first and its second last leaf part. But other leaves are fine. I just duplicated the last leaf to make all those other leaves but somehow only those two are missing faces?? And I have checked the face normals they are pointing outward in the direction they are supposed to. All the trees are having the same problem.
@honey94 Go into blender and flip the direction of the trees Normals
Please Upvote if this help in any way