Disable Terrain Collider but keep trees colliders

I will describe my situation to understand what i need and why.

I have terrain and mesh created from this terrain. (because terrain have bad performance, especially on mobile)
Mesh terrain used to physics calculations of player and enemies as walking mesh.
Terrain not drawing but used as terrain trees holder, because as i found, trees terrains works much better then trees as prefabs (gameobjects), i guess because of tree colliders bake by terrain.
And now i have duplicated colliders, one from terrain, where trees placed and one from mesh terrain.

How to disable terrain collider, but keep trees colliders from this terrain?
Unity 2019.4.36f1

 

In terrain settings, you can define a material. Could create a shader/material that renders nothing.
This may work, as I don't think it will apply to the tree materials.

You can also try toggling the Draw checkbox.

https://docs.unity3d.com/Manual/terrain-OtherSettings.html