What a cool looking shot. As Jacob mentioned, the only thing it needs is to separate the tree from the sky. The dark sky might be done for the mood, but I would brighten it up just a bit more to let the tree stand out more.
I like this quite a bit; looks like something out of J R R Tolkien. The only thing bothering me is the dark upper part of the tree; it looks too much like a split ND filter was used.