This harkens back to my love of the Lord of the Rings. The Ents of LotR were some of my favorite parts of the books. It really brought out the fantasy aspect. Could trees talk? Could we hear them? In addition, I always liked the scene from the Wizard of Oz movie with the trees that attacked. This carried over into my D&D games where my players could meet Treants both as possible friends but also as tenacious enemies.