Exactly. It could be an archer who fires from behind the branches. A mobile firing point. The branches will provide cover, and there will be a firing slit between them. Or maybe it just sits on its shoulder and shoots, or stands in the crown, on top of the tree.
You could put a mage there, but even better would be a warrior. A warrior with a finely crafted spear, for example, so that it has a bonus for running and can reach from behind the branches, or even better with two swords. The tree wraps around and tanks, and the elf creates a bloodbath.
In my opinion, this idea is no worse than the idea of riding a deer or a rabbit.

Lol, okay, as you say.