def uniform_list_length(labels):
    """
    Insert empty string untill all the elements in labels have the same length.

    Examples:

    >>> uniform_list_length([['a'], ['a', 'b'], ['a', 'b', 'c']])
    [['a', ' ', ' '], ['a', 'b', ' '], ['a', 'b', 'c']]
    """
    max_num = max([len(i) for i in labels])
    for label in labels:
        for num in range(1, max_num):
            if len(label) == num:
                label.extend([" " for i in range(max_num - num)])
    return labels