Immolation to damage trees?

Anybody know how to make Immolation damage trees, and destructibles?

I changed the Immolation's "targets allowed" to "Tree," but it still won't work.

Any help would be much appreciated.

Thanks.

I've experimented before and I don't think it's possible. My workaround is to make all trees units.

If you dont want other things that damage units to kill trees make a periodic trigger to pick all nearby destructibles of type tree and kill them

If you want it to do that, make a trigger effect. Make the ability immolation, which doesn absolutly nothing but take away mana, then go, make a trigger that has small area effect. When unit has buff active, reduce the hp of all trees around him by, whatever. I don't know if that is the exact trigger, but i know it has to be trigger spell.