The shadows in the tree branches are darker than the shadow of the tree trunk on the ground. I don't understand that choice.
The tree appears to be designed to stand alone (leaves in rings, lollipop shape, detailed trunk), but the wall of trees in the screen shot would be better served by a forest canopy.
I can only suggest a redesign of the tiles, with an eye towards reuse and combinations to produce a variety of possible trees. Something like vierbit proposed.
Another option would be to make the treetops a seamless leafy glob with only suggestions of individual trees. Since you're trying to convey an impassable forest instead of real trees that one could walk around, this might be ok.
Tourist
edit:typo.