Any clue to set a tree bridge?

Hi, me and my friend trying to figure out how to set a tree bridge so my unit can attack it. I am using the one in Doodads called Tree Bridge (In ashenvale bridge/ramps) I've tryied to make it selectable in game, allowing debris to my unit... Well i tryied many things and we still can'T fix it. Anyone know how?
Thank you!

Did you allowed your unit to attack tree? Cause its probably not a "debris" doodad its a "tree" doodad.

I looked in the object editor and the tree is really classified as a Debris but I still tried giving both debris and trees to my unit and changing the way to Selected as Debris, Tree.I don't know why I can't find how to fix

what about killing the tree through triggers?

yes I just tried a couple of mins ago and yes I got it to work with triggers, it looks pretty cool thanks you