@staticmethod
def _increment_last_level(number):
    """
        Increments the last level in number of the item node.

        :param str number: The number of last node.

        :rtype: str
        """
    heading_numbers = number.split('.')
    heading_numbers[-1] = str(int(heading_numbers[-1]) + 1)
    return '.'.join(heading_numbers)
