input: Write a function to construct an XML document using Python which contains a list of items. The function should take a list of items as input and generate an XML document with these items as sub-elements under a root element named "data". The XML document should be saved to a file named "data.xml".
  
  
  import xml.etree.ElementTree as ET
  
  def construct_xml_document(items):
      # creating the root element
      data = ET.Element('data')
  
      # loop over items
      for item in items:
          # creating sub elements
          item_element = ET.SubElement(data, 'item')
  
          # assign the value for the sub elements
          item_element.text = item
  
      # write the XML Tree
      tree = ET.ElementTree(data)
      tree.write('data.xml')
  
  assert construct_xml_document(['Item1', 'Item2', 'Item3'])
  
output: import xml.etree.ElementTree as ET
  
  def construct_xml_document(items):
      data = ET.Element('data')
      for item in items:
          item_element = ET.SubElement(data, 'item')
          item_element.text = item
      tree = ET.ElementTree(data)
      tree.write('data.xml')