How to use the vis-timeline.DataSet function in vis-timeline

groupEvents[groupIndex] = _.cloneDeep(events);

      // make sure all events have correct group index
      // add only events from groups which still exists
      const points = [];
      _.each(groupEvents, function (events, index) {
        _.each(events, function (e) {
          e.group = $scope.visOptions.groupsOnSeparateLevels === true ? index : 0;
          if (existingGroupIds.indexOf(e.groupId) !== -1) {
            points.push(e);
          }
        });
      });

      data = new DataSet(points);
      timeline.setItems(data);
      timeline.fit();
    };

groups.push({
            id: index,
            content: group.label,
            style: 'background-color:' + group.color + '; color: #fff;'
          });
        });
      } else {
        // single group
        // - a bit of hack but currently the only way I could make it work
        groups.push({
          id: 0,
          content: '',
          style: 'background-color: none;'
        });
      }
      const dataGroups = new DataSet(groups);
      timeline.setGroups(dataGroups);
    };