The tree-like beings in J.R.R. Tolkien's legendarium are called Ents.
Ents are ancient shepherds of trees who appear most prominently in The Lord of the Rings. They live in Fangorn Forest and are led by Treebeard, one of the oldest and most important Ents encountered by the story's characters. Ents resemble trees but can move, speak, think, and act independently.
Their most significant action in the narrative is the Ents' attack on Isengard. After learning from Merry and Pippin about Saruman's destruction of forests, Treebeard calls an Entmoot, or gathering of Ents. The Ents then march against Saruman's stronghold and help destroy his industrial war machine.
Ents are often confused with Huorns, a related but more mysterious group of tree-like beings. Tolkien also drew inspiration from the idea of trees awakening and from literary traditions involving forests, but Ents have their own detailed history and language.