From the Painting Guide: You've captured the essence of the project beautifully with this magnificent tree: the colours on the bark, the strong light, and dark shadows. The glorious yet subtle colours in the branches and in the highlights too, give the tree depth and texture. By contrast, the black shadows at the bottom of the tree are unsubtle and lack variation. It takes a bit of practice to see, but shadows do have variation and colour in them too; for starters I'd add some of the dark brown used in the tree.

I'd also have another look at the where the tree roots (the one next to the red in particular) and ground meet and try and get the roots to emerge more from the ground rather than sitting on top. Though I like the way the line of green trees form a interesting background without competing with the main tree, given the highlights on the main tree, I'd expect there to be some more intense highlights in these.

In terms of composition, I like where you've placed the tree, which gives it place to 'breathe' on the right and at the bottom. If you'd placed it in the centre, it would be a much more static painting.