I think the shading and texturing look great, now you need to get the shape to be a bit more pleasing. Each small clump of leaves is round, and yet your tree is triangular. Additionally there is a big lumpy protrusion coming out the top of your tree and kinda sagging. Here's some references where people made a similarly shaped tree with clumps of leaves like you have:
This one is most like what you have, just if you went around and rounded all the sharp corners as well as "puffed up" any really skinny bunches.
I like this way this one handled the leaves at the edges, they stick out pretty far and are nicely shaped
Unfortunately this image didn't seem to include their entire tree. The gaps and branches in the leaves help with its shape, you could consider doing something like this