Stack and while

def tree(categories, tab=''):
    if type(categories) == 'list' or len(categories):
        stack = []
        tab = ''
        stack.append((categories, tab))
        while len(stack) != 0:
            tmp = stack.pop()
            for category in tmp[0]:
                print tmp[1] + category['name']
                stack.append((category['children'], tab + "--+ "))

categories = [{
        'name': 'Cat 1',
        'children': [{
                'name': 'Sub 1 Cat 1',
                'children': [{
                        'name': 'Sub 1 Sub 1 Cat 1',
                        'children': [{
                                'name': 'Sub 1 Sub 1 Sub 1 Cat 1',
                                'children': []
                            },
                            {
                                'name': 'Sub 2 Sub 1 Sub 1 Cat 1',
                                'children': []
                            }
                        ]
                    },
                    {
                        'name': 'Sub 2 Sub 1 Cat 1',
                        'children': []
                    }
                ]
            },
            {
                'name': 'Sub 2 Cat 1',
                'children': []
            }
        ]
    },
    {
        'name': 'Cat 2',
        'children': []
    }
]

tree(categories)