input: def parse_xml(text: str) -> List[Tag]:
      """ Parses an XML document and returns a list of tag objects.
      Each tag object contains an id and a list of values corresponding to its subchildren.
  
      >>> tag_objects = parse_xml('''<xml>
      ...   <root>
      ...     <child1 id="1">
      ...       <subchild1 value="a"></subchild1>
      ...       <subchild2 value="b"></subchild2>
      ...     </child1>
      ...     <child2 id="2">
      ...       <subchild3 value="c"></subchild3>
      ...       <subchild4 value="d"></subchild4>
      ...     </child2>
      ...   </root>
      ... </xml>''')
      >>> print([(tag.tag_id, tag.values) for tag in tag_objects])
      [('1', ['a', 'b']), ('2', ['c', 'd'])]
      """
  
  class Tag:
      def __init__(self, tag_id: str):
          self.tag_id = tag_id
          self.values = []
      
      def add_value(self, value: str):
          self.values.append(value)
output:     import xml.etree.ElementTree as ET
  
      root = ET.fromstring(text)
      tags = []
  
      for child in root.findall('.//child1'):
          tag_id = child.get('id')
          tag = Tag(tag_id)
          for subchild in child:
              value = subchild.get('value')
              tag.add_value(value)
          tags.append(tag)
  
      for child in root.findall('.//child2'):
          tag_id = child.get('id')
          tag = Tag(tag_id)
          for subchild in child:
              value = subchild.get('value')
              tag.add_value(value)
          tags.append(tag)
  
      return tags