How to segment point cloud and assign IDs to segmented instances？

CesiumJS
1

The Sandcastle demo 3D Tiles Point Cloud Classification highlight different objects in the point cloud using existing object IDs.

classificationTileset.style = new Cesium.Cesium3DTileStyle({
  color: {
    conditions: [
      ["${id} === 'roof1'", "color('#004FFF', 0.5)"],
      ["${id} === 'towerBottom1'", "color('#33BB66', 0.5)"],
      ["${id} === 'towerTop1'", "color('#0099AA', 0.5)"],
      ["${id} === 'roof2'", "color('#004FFF', 0.5)"],
      ["${id} === 'tower3'", "color('#FF8833', 0.5)"],
      ["${id} === 'tower4'", "color('#FFAA22', 0.5)"],
      ["true", "color('#FFFF00', 0.5)"],
    ],
  },
});

My point cloud lacks segmented instance IDs. How can I segment the point cloud and assign IDs to instances?