def print_tree(t, indent=0):
    'Print a representation of this tree in which each node is\n    indented by two spaces times its depth from the root.\n\n    >>> print_tree(tree(1))\n    1\n    >>> print_tree(tree(1, [tree(2)]))\n    1\n      2\n    >>> numbers = tree(1, [tree(2), tree(3, [tree(4), tree(5)]), tree(6, [tree(7)])])\n    >>> print_tree(numbers)\n    1\n      2\n      3\n        4\n        5\n      6\n        7\n    '
    print((('  ' * indent) + str(label(t))))
    for b in branches(t):
        print_tree(b, (indent + 1))
Print a representation of this tree in which each node is
indented by two spaces times its depth from the root.

>>> print_tree(tree(1))
1
>>> print_tree(tree(1, [tree(2)]))
1
  2
>>> numbers = tree(1, [tree(2), tree(3, [tree(4), tree(5)]), tree(6, [tree(7)])])
>>> print_tree(numbers)
1
  2
  3
    4
    5
  6
    7
def print_tree(t, indent=0):
    'Print a representation of this tree in which each node is\n    indented by two spaces times its depth from the root.\n\n    >>> print_tree(tree(1))\n    1\n    >>> print_tree(tree(1, [tree(2)]))\n    1\n      2\n    >>> numbers = tree(1, [tree(2), tree(3, [tree(4), tree(5)]), tree(6, [tree(7)])])\n    >>> print_tree(numbers)\n    1\n      2\n      3\n        4\n        5\n      6\n        7\n    '
    print((('  ' * indent) + str(label(t))))
    for b in branches(t):
        print_tree(b, (indent + 1))