this is great, but since you request critiques, I'll try and find something constructive that can make this already sublime piece of art slightly better..
What you could do is position the treant a bit more to the 2/3 mark. at the moment he hovers somewhere around the middle and the golden ratio. I also think that the right arm could have a better pose. also, changing the eyes to match the color of the flame would improve it. Right now They look different from the flame.
But nontheless, I love this work. The color is well-chosen and balanced, and the treant design looks very good, even with the lack of feet. And the execution is very well-done.