I Need help with trees colliding

for the mouse cursor, try this:

// Hide the cursor
Screen.showCursor = false;

collide with trees: If you use the terrain engine and create trees on the terrain, there is the option "Create Tree Colliders" Link Unity Documentation: Trees

If you create your own trees and import them, you could add mesh colliders or a simple geometry collider like a capsule collider. Check this documentation link where it mentions colliders.

EDIT:

You are correct that the standard palm tree out of the box doesn't work for me either. The following worked for me though:

Import a tree which you would like to place on your terrain. Apply a capsule collider to it (according to the tree collider link above, only capsule colliders work for this). Convert the object to a prefab. Select the prefab as a tree for your terrain and place it. I couldn't really do the same with the standard palm tree that comes with your unity install, because it wouldn't let me add a capsule collider to the palm prefab. But hey, you might wanna create your own beautiful trees anyways.