input: 
  def create_xml_document(items: List[str]) -> str:
      """Construct an XML document in Python that contains the given list of items. 
      The XML document should have a root element named 'data' and each item 
      should be a sub-element named 'item'.
      The function should return the XML document as a string.
      >>> create_xml_document(['Item1', 'Item2', 'Item3'])
      '<data><item>Item1</item><item>Item2</item><item>Item3</item></data>'
      """
  
output:     xml_string = '<data>'
      for item in items:
          xml_string += f'<item>{item}</item>'
      xml_string += '</data>'
      return xml_string