tree.py

class TreeNode:
    def __init__(self, data):
        self.data = data
        self.children = []
        self.parent = None

    def add_child(self, child):
        child.parent = self
        self.children.append(child)

    def get_level(self):
        level = 0
        p = self.parent
        while p:
            level += 1
            p = p.parent

        return level

    def __str__(self):
        spaces = " " * self.get_level() * 3
        prefix = spaces + "|--" if self.parent else ""

        tree = prefix + self.data + "\n"

        if self.children:
            for child in self.children:
                tree += child.__str__()
        return tree