i feel like it's a bit sketchy and undefined, it kind of has that look of having the shading kind of sketched on with a one-pixel brush and not actually tightened up at all. which is fine if it's what you're going for, but it kind of gives the feeling of an unrefined piece.
i do like the general knobbly look of the trunk and branches, though. but it's a little strange that the only branches you have going on are a. thick with big bushy leaves, and b. one pixel wide with tiny leaves. no inbetween, you know what i'm saying?
looking at it again, there's a lot of one pixel dots all over the darker parts of the tree. it really does lend to that feel of having been sketched without any real polishing. imo spend some time smoothing out the edges in your shading and refining it, and maybe look up pics of trees to help you with the branches. i really like the topmost branch with all the littler branches coming off of it.
The colors remind me of good old times... which palette is this ? Looks a bit like the Paint palette...
Noce style though...
You're going to the right way, keep refining.