I really like the idea, and it almost works - as you're hearing, I think the crop on top and along the bottom is too much. I want to see just a little space above and below the branches, just as I do on the side. It looks really good, otherwise - great idea.
Yeah, 50mm can be a tricky focal length. Right in between the wide angle that you need when you can't back away from your subject, and the telephoto that is useful when you're too far away. But it's a great tool for learning with, and it's always better than having a telephoto lens when you need wide angle, or vice versa.
As the others said the composition is a little lacking but I really like the sharp scrolling lines of the branches. It might make an interesting absract with an even tighter crop.