input: Write a function to construct an XML document using Python which contains the given list of items. The function should take a list of strings as input and generate an XML document with a root element named 'data' and sub-elements named 'item' for each item in the list. The XML document should be saved to a file named 'data.xml'.
  
  import xml.etree.ElementTree as ET
  
  def construct_xml_from_items(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')
  
  assert construct_xml_from_items(['Item1', 'Item2', 'Item3'])
  assert construct_xml_from_items(['Book', 'Pen', 'Notebook'])
  assert construct_xml_from_items([])
output: import xml.etree.ElementTree as ET
  
  def construct_xml_from_items(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')