This is a small tool to visualize a tree 
structure.

You should write the following functions for the draw_tree
function to use:

get_tag          : return the node name to print
iter_children    : get the children
is_leaf          : check if the node is a leaf

It depends on PIL

Right now, there are two example to use this little tool:

htmltree.py htmltree.jpg which draws a dom tree
listtree.py listtree.jpg which draws a list presented tree