Oscarito:
It has been a long while since I started modding maps, so bare with me and mistakes here..
But..are you adding the trees in the Mission builder by chance? I would try to do it in the FMB+, the map making version.
You will find tips how to use the FMB+ in the map making section here..
You need Boomer's map making kit..
http://ultrapack.tuttovola.org/index.php/topic,1977.0.htmlIn the FMB+, you can easily scroll through various trees and bushes in the "objects" list.
The objects are actually named THERE as opposed to the annoying object number list in the normal mission builder. Helps a lot.
I still have a hard time (agracier once explained it IIRC) to get how various random trees are assigned in IL-2, but we already have a number of kickass trees here, including hi resolution trees (prolly not what you search for atm).
To close, it is always better to add objects in the Full Mission Builder Plus than in the Mission Editor, saves framerates, AFAIK.
You only need the dedicated config.ini entries and the dedicated bldconf.ini file for the FMB+.
And a maps folder in your main install to save the changes..
See Up~Boomer's thread..
OK...good Luck!
Tom