ifor.py

def ifor(*lists):
    root = Node('ROOT')
    for L in lists:
        leaves = list(root.leaves())
        for data in L:
            # create once, use multiple times
            # this way we end up with a graph, instead of a tree
            new_node = Node(data) 
            for leaf in leaves:
                # leaves() function may return same nodes multiple times
                if not new_node in leaf.children:
                    leaf.add(new_node)
    return root.routes_to_leaves()