Definition of "treeish"

The treeish thing looked stiff and clumsy, but it wasn't; it was fast and flexible and frighteningly strong.

1986, Jo Clayton, The Soul Drinker, page 343

In The Lords of the Rings there are dark forces in the forest—the Huorn. Huorn are ents who have become more treeish, gone rogue. They can still move and speak, but only with the ents.

2017, Inga Simpson, Understory‎, Hachette UK