input: def parse_xml(text: str) -> List[Tag]:
      """Parse an XML document and return a list of tag objects.
      Each tag object is an instance of a custom Tag class that stores the id and values of the subchildren.
      >>> xml_text = '''
      <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>
      '''
      >>> tags = parse_xml(xml_text)
      >>> [tag.tag_id for tag in tags]
      ['1', '2']
      >>> [tag.values for tag in tags]
      [['a', 'b'], ['c', 'd']]
      """
      import xml.etree.ElementTree as ET
      
      tag_objects = []
  
      root = ET.fromstring(text)
      for child in root:
          tag = Tag(child.attrib["id"])
          for subchild in child:
              tag.add_value(subchild.attrib["value"])
          tag_objects.append(tag)
  
      return tag_objects
  
  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
      
      tag_objects = []
  
      root = ET.fromstring(text)
      for child in root:
          tag = Tag(child.attrib["id"])
          for subchild in child:
              tag.add_value(subchild.attrib["value"])
          tag_objects.append(tag)
  
      return tag_objects
  
  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)