Print Binary Tree - Python

[Daniel94]

def show_2d(self):
    '''
    Show a pretty 2D tree based on the output of bfs_order_star(). None
    values are are replaced by stars ('*').

    For example, consider the following tree `t`:
                10
          5           15
       *     *     *     20

    The output of t.bfs_order_star() should be:
    [ 10, 5, 15, '*', '*','*', 20 ]
    '''

I already got the function bfs_order_star() working like it should. That is a function that returns an array with all of the nodes from a tree in breadth-first traversal, where the empty nodes are declared as '*'.

Any ides how I can write a function that prints a 2D tree based on the data from that array?