If I understand correctly, are you basically layering horizontal sections of it instead of thinking of it as a sphere? Looks like your view is more of a top down view than mine. I think we both shaded it the same way though, I just sketched the whole thing out and did the shadows and then highlights but I was probably imagining it differently. I'll try that style too.
Ermm, I'm fairly poor at explaining myself, so I made pictures rather!
This is more or less how I would have shaded the tree ignoring bunches:
And then using the following technique I'd add bunches:
Starting with a simple round tree with simple shading.
Drawing an imaginary ellipse where a bunch should be.
Then, using the colours afforded to me by the larger shading (and adding a little more to both the high and low lights) I'd make bunches.
Mine was a bit more top down yeah, and I should also mention that the bottom half of your tree is shaded perfectly, you just needed more "volume" in the top half. Which just means less dark colouring because the higher part of the tree you'd expect to be a lighter colour on the whole (though actually if you look at tonnes of pictures of trees you wouldn't see that). That way the tree looks more solid (which again, they aren't IRL, but we're tricking eyes here, not going for realism).
I
think.
