I don't exactly understand what this is. It's a background/environment for a 2D video game? Is this just one side? I don't see anything resembling a sandbox.
I gather you're going for a quirky, cartoony style, but the houses could fit a lot better into the tree. They don't really relate at all, they're just stuck on. It's a little weird that the branches are growing straight sideways or even downward. The way you have the tree cut out and the shadow around the base makes it look like it's floating. you can even see traces of sky beneath the roots.
Thanks for you advice, I see what you say. It's for a 3d game btw. This is only the tree side! I chose to use a dead tree, there is no green and will stand out between the forest that will come along with it. (there is no reference in this image about a forest yet but there will be)