Gantt Tree grid parent

HTML

<script src="https://code.highcharts.com/highcharts.js"></script>
<script src="https://code.highcharts.com/gantt/modules/gantt.js"></script>
<script src="https://code.highcharts.com/gantt/modules/exporting.js"></script>
<div id="container"></div>

CSS

#container {
  max-width: 1000px;
  margin: 1em auto;
}

JavaScript

// THE CHART
Highcharts.ganttChart('container', {
  title: {
    text: 'Upload for waterfall123'
  }, 
  xAxis: {
  	/* tickInterval: 1000, */
  },

  series: [{
    name: 'waterfallid123',
    data: [
      {
        name: 'upload.client.startcall',
        start: 1546634577918,
        end: 1546634579111
      },{
      	// parent task
        name: 'upload.client.transcode',
        id: 'transcode123',        
        // hide the subtasks
        // collapsed: true,
        
        start: 1546634685408,
        end:   1546634698680,
        // use a smaller pointwidth for the parent task 
        pointWidth: 20
      }, {
        parent: 'transcode123',
        id: 'transcode1',
        name: 'transcode segment',
        start: 1546634685419,
        end: 1546634689408,
      }, {
        parent: 'transcode123',
        id: 'transcode2',
        name: 'transcode segment',
        start: 1546634689408,
        end: 1546634691408,
      }, {
        parent: 'transcode123',
        name: 'transcode segment',
        start: 1546634691408,
        end: 1546634697680,
      }
    ]
  }]
});