I love the concept, but it all looks a bit noisy, especially the tree. Instead, try to think of the trunk as a cylinder. Where is the light coming from (=where to the broad shadows and highlights go?), what sort of shadow does Lara Zomft cast on it? Then, you can suggest the tree's bark texture by making the edges of those shadows and highlights textured rather than smooth.
You can create deeper textured by breaking up the lights and shadows entirely, but you should avoid doing too much of this (i.e. leave some flat areas), and it's generally a good idea to avoid having your lightest and darkest colours right next to each other unless you have a specific reason for it.