I really like the shape of the tree. The shading of the trunk could probably be smoothed out a bit to better fit the rest of the tiles which are super simple, though. It comes off as too busy in comparison, though the leaves are great.
Good point about the tree; that was one of the first tiles I did, so I might go back and address that once I start tiling in earnest. Right now, I've been focusing on monster design, but tiling isn't that far down on my list.