Shade the bottom right side (the direction it is moving) just on the edges and taper it off as you go in. Not a lot of shading though. Aslo, I would suggest smoothing out and rounding the front of the fireball more using the line tool. You can really tell you brushed it with how jagged it is in some spots. Makes it look sloppy.
the top branches look too perfect in comparison to the imperfect trunk, I would make them (the top branches) more skewed rather than perfectly straight
There's not really a correct way. If you aren't sure how to draw something don't rely on memory and draw what you feel is right. Gotta look at real trees or whatever it is instead of trying to wing it.
For what youre going for in that track I would look at examples of cartoon trees from there get a general idea of how you want to draw yours