I think you overdid it.
buy having small bunches like that you have made it a bit flat. if you look at JJ Naas you'll se the kept it very smooth in the transitions. on the top area its overal bright and you'll see that there's harly any really dark areas, thus making it look like there not holes or bumps. as it goes down and bends inwards, it gets darker. if you do several dark areas, you make it look like the tree has loads of bumps. and insteand of following this big tree top shape, you kind of make it look like a pile of bumps. and since they are shaded the same, they look like they are on the same plane = flat!
