With your setting trees where still showing...But I don't have Pur be I am 100% sure many tested it with Pur.Unsure how the Far Plane changed to that,I dont even remember changing that,as im not even sure what it does,unless it had something to do with mods I downloaded from before..
I checked in the cache folder,I dont have the trees_data folder there at all,all I got in there is a trees_alignment folder,and in that only has ks_nordschleife__touristenfahrten.bin and la_canyon.bin.
Graphics wise,Im just using the reality pro 2 filter from RD with very minimal adjustments in pure other then set it to max.
Video Settings: https://acstuff.ru/s/SvZOZL
I changed the farplane settings,still see no trees.
I would go to CM-Settings CSP > About and hit delete patch and then hit install 0.1.79
OR
Disable SOL CM>Assetto Corsa > Video and uncheck Pos-Processing.
You might want to try imola 1994 and see if you have 3d Trees.
Keep me posted!
Bonne chance!