Something that immediately catches my attention on the tree is the shadowy grass around it. "Well duh, the leaves are casting a shadow over that area," you say. But look at the roots. Do they not possess an apparent highlight? This light source is apparently very selective in what it hits. 
Sarcasm aside, that lighting inconsistency is a bit worrisome. I like what you've done with the feel of the roots, but they need to actually come together and form a real structure. The way they converge now feels flat, and the tree is lacking its classic cylindrical feel. What perspective are you going for?
The left-hand bunch of leaves is a step in the right direction, but you need to make the dithering more random. Mix in some darks with the lights to give it a more inconsistent look. Trees don't have really thick parts like that unless you're in the Amazon. The grass at the base of the tree looks great as is, no crits.
So basically, your lighting needs to be more consistent, the base of the tree needs to be more believable, and the leafy sections need to be shaped more like the left hand side with some better, more organic dithering thrown in. Sorry if I sound too negative; it's actually not bad looking. It just needs a little more "oomph". Oh yeah.. hue shifting can help with that too, but it won't fix fundamental form errors.
First thanx for the replay.
So you say:
- there needs be more structure at the roots and no highlights.
- the leaves need be more detailed with hue-shifting,randome dithering,darker colours.
But, i'm new to hue-shifting, i dont realy know good how to use and how to do it, i've readed the colour topic but with the hue-shifting hard to understand can you give me some addvice for it?
Ill try work on the roots
edit: (dont got time for the roots i've to study right now for a test but i think this is way better)
new - old
