Tree Kin

The forest spirits of Athel Loren may take up permanent residence inside trees to become the wise and powerful creatures called Treemen, or they may temporarily animate the dead husks of trees for short-term, often violent ends. When still, Tree Kin appear to be normal, dead, eight-foot tall trees, but when animated they become grotesque parodies of Men, with corpse-like faces in their bark and branches jutting from their bodies at improbable angles.

Source

 * Warhammer Fantasy RPG 2nd ED -- The WFRPG Companion (pg. 126).