This looks like a made up tree, is it? i see a lot of pattens that look suggested. The lighting and cast shadows don't make a lot of sense. especially as there is no cast shadows on the free itself. from that angle those branches would be casting streaks across the tree itself, as well as the ground. a lot of beginners seem to think cast shadows only exist on the floor. Telling the truth trees are bloody difficult to draw. If you want to get better i would suggest rendering simple planar shapes and rendering fruit and more basic objects. there is a lot of complicated form changes in a tree, not to mention texture and opacity from the light passing through the leaves. Hope that helps.
This is a good place to study aswell -
http://www.conceptart.org/forums/sho...d.php?t=223686
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