Hi!
Firstly, i m sorry my bad english 
I added palm trees on my terrain. But i didnt mesh collider into trees. My car is pass through them. My understanding english is better than writing it.
Help me please!
Photo is here. Thank you.
You need to add a primative collider to your trees, not a mesh collider. Your trees are very cylindrical in their trunk design so use a capsule collider instead. If you trees are placed via the terrain tool then you might have to redo them all once you have added the collider to the prefab. Does your car have a mesh collider on it, if it does then you need to make sure it is set to convex or better still approximate the shape of the car using primatives(Box colliders). Non convex Mesh Colliders are for static objects.