input: Write a function to create an XML document using Python which includes the specified items. The function should accept a list of items and generate an XML tree that contains each item as a sub-element under the root element named "data". The XML document should be written to a file named "data.xml".
  assert construct_xml(['Item1', 'Item2', 'Item3'])==None
  assert construct_xml([])==None
output: 
  def construct_xml(items):
      from xml.etree.ElementTree import Element, SubElement, tostring
      root = Element('data')
      for item in items:
          SubElement(root, 'item').text = item
      with open('data.xml', 'wb') as f:
          f.write(tostring(root))
  