How to use the gpxpy.gpx.GPXTrackPoint function in gpxpy

"""
    name = origina_filepath.split('/')[-1]
    for i, segment in enumerate(segments):
        label, points = segment
        filename = label + '.' + str(i) + '.' + str(len(points)) + '.' + name.split('.')[0] + '.gpx'

        gpx = gpxpy.gpx.GPX()

        gpx_track = gpxpy.gpx.GPXTrack()
        gpx.tracks.append(gpx_track)

        gpx_segment = gpxpy.gpx.GPXTrackSegment()
        gpx_track.segments.append(gpx_segment)

        for point in points:
            gpx_point = gpxpy.gpx.GPXTrackPoint(
                latitude=point['lat'],
                longitude=point['lon'],
                elevation=point['alt'],
                time=point['time']
            )
            gpx_segment.points.append(gpx_point)

        save_file(folder, filename, gpx.to_xml())

LineString -> add all Points in a Route
        Polygon -> add all Points of the external linering in a Route
        Collection (of LineString or Point) -> add as a route, concatening all points
        """
        if isinstance(geom, GeometryCollection):
            for i, g in enumerate(geom):
                self.geomToGPX(g, u"%s (%s)" % (name, i), description)
        elif isinstance(geom, Point):
            wp = self._point_to_GPX(geom)
            wp.name = name
            wp.description = description
            self.gpx.waypoints.append(wp)
        elif isinstance(geom, LineString):
            gpx_track = gpxpy.gpx.GPXTrack(name=name, description=description)
            gpx_segment = gpxpy.gpx.GPXTrackSegment()
            gpx_segment.points = [self._point_to_GPX(point, klass=gpxpy.gpx.GPXTrackPoint) for point in geom]
            gpx_track.segments.append(gpx_segment)
            self.gpx.tracks.append(gpx_track)
        elif isinstance(geom, Polygon):
            self.geomToGPX(geom[0], name, description)
        else:
            raise ValueError("Unsupported geometry %s" % geom)

def write_gpx(path, data):
    gpx = gpxpy.gpx.GPX()
    gpx_track = gpxpy.gpx.GPXTrack()
    gpx.tracks.append(gpx_track)
    gpx_segment = gpxpy.gpx.GPXTrackSegment()
    gpx_track.segments.append(gpx_segment)
    for point in data:
        gpx_segment.points.append(gpxpy.gpx.GPXTrackPoint(
            point[1], point[2], elevation=point[3], time=point[0]))
    with open(path, "w") as f:
        f.write(gpx.to_xml())

if len(gpx_content.tracks) == 0:
        return None

    track_segment = get_gpx_segments(
        gpx_content.tracks[0].segments, segment_id
    )

    gpx = gpxpy.gpx.GPX()
    gpx_track = gpxpy.gpx.GPXTrack()
    gpx.tracks.append(gpx_track)
    gpx_segment = gpxpy.gpx.GPXTrackSegment()
    gpx_track.segments.append(gpx_segment)

    for point_idx, point in enumerate(track_segment[0].points):
        gpx_segment.points.append(
            gpxpy.gpx.GPXTrackPoint(
                point.latitude, point.longitude, elevation=point.elevation
            )
        )

    return gpx.to_xml()

def write_gpx(path, data):
    gpx = gpxpy.gpx.GPX()

    gpx_track = gpxpy.gpx.GPXTrack()
    gpx.tracks.append(gpx_track)

    gpx_segment = gpxpy.gpx.GPXTrackSegment()
    gpx_track.segments.append(gpx_segment)

    for point in data:
        if len(point) > 3:
            gpx_segment.points.append(gpxpy.gpx.GPXTrackPoint(
                latitude=point[1], longitude=point[2], elevation=point[3], time=point[0]))
        else:
            gpx_segment.points.append(gpxpy.gpx.GPXTrackPoint(
                latitude=point[1], longitude=point[2], time=point[0]))

    with open(path, "w") as f:
        f.write(gpx.to_xml())  # loosing milliseconds here

def path_to_gpx(path, filename=None):
    gpx = gpxpy.gpx.GPX()

    # Create first track in our GPX:
    gpx_track = gpxpy.gpx.GPXTrack()
    gpx.tracks.append(gpx_track)

    # Create first segment in our GPX track:
    gpx_segment = gpxpy.gpx.GPXTrackSegment()
    gpx_track.segments.append(gpx_segment)

    gpx_segment.points = [(gpxpy.gpx.GPXTrackPoint(lat, lon, time=time)) for (lat, lon, time) in path]

    if filename:
        with open(filename, 'w') as gpx_fh:
            gpx_fh.write(gpx.to_xml())

    return gpx

tree = etree.fromstring(content)

    for track_point in tree.xpath("//ns:trk/ns:trkseg/ns:trkpt", namespaces=NS):
        latitude = float(track_point.get("lat"))
        longitude = float(track_point.get("lon"))

        elevation = track_point.xpath("ns:ele/text()", namespaces=NS)
        elevation = float(elevation[0])

        point_time = track_point.xpath("ns:time/text()", namespaces=NS)[0]
        # e.g.: 2018-04-28T14:30:50.000Z
        point_time = gpxpy.gpxfield.parse_time(point_time)

        # print('latitude', latitude, 'longitude', longitude, "elevation", elevation)
        point = gpxpy.gpx.GPXTrackPoint(latitude=latitude, longitude=longitude, elevation=elevation, time=point_time)
        gpx.tracks[0].segments[0].points.append(point)

    return gpx