I just have aproblem with lineart, I think the trunk becomes too small for the roots that you made, you can change it by expanding the mid/upper trunk area and adding more leaves. There si actually a pretty abdass tutorial on trees at:
http://petesqbsite.com/sections/tuto...o/chapter5.htm
If you are interested. (I mean from your work it kind of looks like you know what you are doing).