The sky on this is just beautiful, and I like the way the tree is sihouetted against it. The cloud formations add a bit of drama to the sky as well. If you don't mind a suggestion, I think if you were closer to the ground so the tree could be completely sihouetted, and possible moved a bit to the left so the tree is a bit less centered it would improve the composition.
I find it so difficult to strike the right balance between a light sky such as this and the darkness of the ground--something seems always to be over or under exposed. With a shot like this, I usually try to reduce the amount of ground so I can preserve the richness of the colors in the sky.