The Tree People are a species of wood-like people who appear in "When Wedding Bells Thaw" and "It Came from the Nightosphere." They resemble humanoids made of wood or trunks of trees.
In "When Wedding Bells Thaw," a tree person punches Ice King in the face because he spits his drink out on him while partying. That specific tree person had a PHIL FACE.
In "Another Way," evergreens with eyes and mouths watch Finn running away screaming. Finn encounters Talking Bush and Tree Stump With Sign in this episode.
Tree People in "When Wedding Bells Thaw"
Trees in "Another Way"