docs: def export_gpx_file(self):
          """Generate GPX element tree from ``Trackpoints``.
  
          Returns:
              etree.ElementTree: GPX element tree depicting ``Trackpoints``
                  objects
          """
          gpx = create_elem('gpx', GPX_ELEM_ATTRIB)
          if not self.metadata.bounds:
              self.metadata.bounds = [j for i in self for j in i]
          gpx.append(self.metadata.togpx())
          track = create_elem('trk')
          gpx.append(track)
          for segment in self:
              chunk = create_elem('trkseg')
              track.append(chunk)
              for place in segment:
                  chunk.append(place.togpx())
  
          return etree.ElementTree(gpx)