Treefolk live in their trees and never move away from them. They generally look like the tree they live in. If you see a tree that looks like it has a face through the knots in it, then a tree person may live there. You can also check for roots that are above ground and loose dirt or overturned moss. Treefolk may grown in the center of a faerie ring. The treefolk dies when the tree is cut down. Oak, ash, single thorn and female holly treefolk are believe to be protective. Oak is sacred to the faeries and the most powerful is rowan. These treefolk are also the most friendly. Holly treemen are considered to be dangerous as well as hawthorn treefolk that are in groups of 3 or more. Hazel treefolk are wise and can pass their wisdom on through their nuts. Apple treefolk give power and youth, but there is a danger of being carried away by faeries if you sleep under an apple tree. 
* photo courtesy of Arthur Spiderwick's Field Guide