Some of the falling trees fall on you (... yes, I know, this is what they are meant for...), although you shoot them.
The unfortunate victim will turn yellow (instead of the usual blue selection box) before being killed.
NO PROBLEM !
Just destroy the tree from the other side !
This level is really far easier than it seems. Save the game regularly, but you can end it with all AT-PT and most of your Troopers....