1.- make a back up of the track
2.- unrar the content of the "imola_3d_tree.rar" inside ---- \Steam\steamapps\common\assettocorsa\content\tracks\imola\
Fenryr released 1.4 version of Imola as 2024 standalone and your trees don't work anymore, although before that they worked on 1.3 version.
Could you please revised this?
UPD: Sorry for that, It was my mistake - I forgot to put the trees folder in extension. All works fine!