Thanks for the feedback. I'll keep those tips in mind for my next attempt at a tree.
As for why I didn't post in the forums, I couldn't login to the forums because i needed 6 points in the gallery so I posted these to get those points.
Thumbnails should be pixel art too. This means no blurry scaling. You can crop instead.
Are these WIP steps of the same tree, or different trees that all have the same shape?
Since it looks like you're iteraring in any case, I recommend posting on the forum instead of submitting them to the gallery. You're more likely to get feedback that way. In addition, submissions that look like WIPs may not be accepted to the gallery at all.
When you draw trees, start with the branches. Even if you don't include them in the final art, they'll help you imagine how the tree is structured.
When shading foliage, remember that it's not all one mass of leaves. It's a bunch of branches that all come together to make an irregular whole. Shade those 3D clumps, not the 2D shape of the overall crown. Some parts come out clsoer to the viewer, some parts are further back.
To create leaf texture without making your piece look very noisy, suggest it at the edges of your colours instead of scattering single pixels or small clusters around everywhere. As long as you create the impression of there being leaves in various places, it's fine if most of the image is actually completely flat - the viewer's brain will fill in the details.
Also, it's okay to fudge the scale a little for the sake of clarity and aesthetics - even if the leaves would be ~1px each at this scale, it'll probably look better if you draw them as larger clusters. If you do the boundary trick instead of drawing individual leaves, it won't even be noticeable that they're not to scale, because they'll read as clumps of leaves rather than individual leaves.
You can get points by commenting and rating other pieces.