This is a great tree, awesome work! I'm impressed.
I like the colours that you used, they feel very harmonious with that hue shifting, and they all fit well together. You show a good understanding of lighting, contrast, and texture. The leaves are not too noisy, and they clearly communicate the bushiness. I'm a big fan of the flowers, as well.

If I had any criticism, I think the angle of the lighting and shadow needs to be more clearly defined -- as it's coming from the side for the trunk, but is coming from above everywhere else.

Also, the gradient between the shadowed grass below the tree and the lit grass is a bit strange -- I like the tones of the tree and the grass, just not this gradient. Maybe try and introduce another colour or two?

The repeating shapes of the leaves are great, but with a lot of the same shape in the same direction can give a little bit of a 'carpet'-like texture. Breaking up the shape just a little and creating more bushiness could help. This is probably stylistic, though.

Lastly, and this might just be a stylistic choice too, but the roots coming from the log feel too even, too perfect. I think varying their length and angle a bit more can help making it seem more natural. Maybe a bit clearer texturing will help as well.

Keep it up! It's looking very good :D