There's something I like about the various sizes and shapes of the leaves you drew, but I can't imagine a good excuse for one tree to feature what seems to be a variety of leaves. Vine overgrowth, maybe? The canopy looks a bit too much like a big, green glob of dough to me. You might consider breaking into the edges, makng the outline a little jagged, to show some leaves overlapping one another. Also, instead of just "checkerboarding" the pixels on the trunk, you might think about using them to make wiggly vertical lines to simulate a bark texture. A tree that size could probably use some substantial roots to hold it up, too. By that I mean the bottom of your trunk just looks like a rounded off nub, it doesn't look planted, just balancing unwieldily on that rounded bottom.