Alrighty amigo, here’s the issue and a fix!
The difference between your collision mesh in Blender and in UE4 is happening because all UE4 collision meshes must be entirely convex. See this article under the Collision section for more detail: UE4 FBX static mesh pipeline. When you import your collision into UE4 it is converting your mesh into an entirely convex one.
The way to make this work is to split your collision mesh in Blender (UCX_Tree) into multiple convex meshes. For instance, separate each bunch of leaves, the two branches and the trunk into individual meshes. For naming, you can add _# to each mesh (i.e. UCX_Tree_1, UCX_Tree_2, etc.). You can do some different naming conventions too, but Blender’s standard .### for duplicates doesn’t seem to work (unless you put an underscore first).
Let us know if that helps and works for you.
Nice tree by the way. Very fun.
Cheers and have a rootin’ tootin’ awesome day,
-Noah