Change physics

There was a video on YouTube that I can't find anymore which showed how you can change the physics if you drive into a tree that instead of breaking through it like dust, the tree stays intact but just falls down

I know it's done in the P3D editor to change whichever zone .P3D file the tree is in, such as l1r1.p3d, but inside that file I don't remember what exactly to do from there

Thanks