2 questions with rendering and collision! Anything helps

Hello ladies and gentlemen!

So take a look at this image to have a better visual of my issues.

First question being rendering, why is it when i play the template the trees have their collision fully shown not just the visual parts? some of the trees are fully rendered but the rest are not, how do i fix this?

Second question is about the rocks. As you can see, my legs are inside the rock, but im not fully falling through them. How would i fix this so the collision is at the surface of the rock, rather than a little inside?

Thank you, and anything helps!

Your billboard LOD is probably using the wrong material slot.

Im not sure what that means, can you elaborate?

In the static mesh preview window, the last LOD (Level of Detail) looks like it is set to a branch/bark material rather than the billboards material.