Yes, eventually I've added the Eat Tree ability.
The idea is this, you use the eat tree ability to eat the tree (take it's life energies, if that sounds better) and then you use the item on yourself to cast the ability restoring your health, resulting in the lose of 1 charge.
To do this I've added two abilities to the idem, and I detect which one of them is used so the proper effects happen. Abilities share the cooldown and order id, so this works well.
What kinda bothers me is that once the item has no more charges, it can't be used, and the icon doesn't show the charges indicator (bottom right part of the icon). So, I need to keep the item at 1 charges at all time.
Basically, you need 1 charge to chop a tree, and minimum 2 charges to heal your hero.
I can't think of a way to make this better.