You need more value shifting on a large scale - right now your values are only used to define texture/detail, you need a larger sense of form too, think about the BIG leaf ball and where light would hit it as such, then combine it with the texturing. It's hard but you'll figure it out.
Don't use all of your shades everywhere. Also don't make your tree look like a green mass with big dark lines through it. the upper 'good' tree (with the green check mark) looks very iffy to me, the one below it is myck more on the right track.
Just go go go, I like your tree. I love trees. I don't mind that everyone is making a tree right now! : D
... I wanna make trees too.
