Tree of Aeons

This is a reincarnation/isekai story, about Matt (later TreeTree), an overpowered tree in a fantasy world that serves as the battlefield for an ongoing conflict between demons and the heroes summoned to oppose them.

At first a bystander, over a long period of time, TreeTree will learn all sorts of skills, gain levels, and in doing so, build up a forest, train young subordinates, protect a village, and more.