Tree & Giant, all in one. The treant is of course based on the concept of the ent, which came from Tolkien bu tin this case Tolkien was again borrowing from mythology and improving on the idea. Gary Gygax, inspired by Tolkien included the concept of the tree giant, the sentient tree in his world of Dungeons and Dragons – calling it the treant – a merger of the words tree and giant..
The Tree of the Sun and the moon figures heavily in Indian mythology. This tree told the future. Different parts of the trunk spoke at different times of the day. In the past such actual people like Marco Polo and Alexander the Great are said to have spoken to this tree. In Greek and Roman culture the concept of oracles is a huge part of their mythology. Many trees seem to have this oracular ability. And, back in the good old UK it is said that some trees in Ireland will help people looking for a Leprechauns gold. Sometimes it is simply a nod to the location but sometimes it can also be much more direct where the tree actually tells the location.
large Man-like, almost Troll-like, figure, at least fourteen foot high, very sturdy, with a tall head, and hardly any neck. Whether it was clad in stuff like green and grey bark, or whether that was its hide, was difficult to say. At any rate the arms, at a short distance from the trunk, were not wrinkled, but covered with a brown smooth skin. The large feet had seven toes each. The lower part of the long face was covered with a sweeping grey beard, bushy, almost twiggy at the roots, thin and mossy at the ends. But at the moment the hobbits noted little but the eyes. These deep eyes were now surveying them, slow and solemn, but very penetrating.
In the movies, the attack of the ents on the fortress of Sauroman is a spectacular moment in the Two Towers.
The treant is the D&D concept of the ent or talking tree. Though in this case the treant can take on a much darker life, depending on the GM and the campaign that you are running. Of course, they are not the only game to bring the concept of the treant into a game. Warcraft III had treants that could be turned loose if you were playing the elves. These lodges of the elves could be animated and turned loose on your foes.
All in all, the concept of a walking talking, possibly fighting tree is a throwback to the mythology of old. The people of our ancestry saw nature in an entirely different way then we did and it is possible that they added to the concepts of their mythology due to some old gnarled giant that they saw in the woods near their cities. A face in the bark, a certain movement when the wind blew may have given that tree more human characteristics