Dithering only really works if you can cover a large enough area with it. What you've done reads more like a few additional lines rather than dithering. That said, I think it is a step in the right direction, as it breaks up the artificial-looking horizontal lines, turning them into diagonals.
I think you're focusing a bit much on the sections of bark, I'd weaken them by breaking up the lines, and I'd instead create texture with rougher cluster edges.
(I also added some thin branches, as the tree looks unnaturally tidy to me without them.)
