I tried to do another tree. And pretty much failed...
1st version after maybe 20 minutes:
and then I "refined" it and made it worse and the real problem for me is that I don't exactly understand why it looks worse then the first version. I mean there are less pixels then leaves on a decent tree - how am I supposed to pixel branches and leaves?
Also, you might not see it but the perspective is meant to have a 45° angle (whatever the correct term for that is) but all two versions of the tree (just like the first one post above) look flat and as if viewed from a much lower angle.
Critizism and tips very welcome. Don't restrain yourself - i have no feelings towards this tree and my artistic skills in general that you could hurt!