Branch start/end angle and distribution are the main factors that will effect the shape of the tree. Distribution will effect the vertical pattern of branches i.e. uniform from top to bottom, clustered toward the top. Branch start angle effects the "offshoots of the branches. This will control if they point up, down or sideways. Branch end angle effects the leafy part of the branch and to what degree it bends. it is similar to gravity but it is a more precise and uniform control. Look at the brycetech treelab thingymabobber.