yout extends go.TreeLayout {
    constructor(init) {
      super();
      if (init) Object.assign(this, init);
    }

    makeNetwork(coll) {
      const net = super.makeNetwork(coll);
      // copy the collection of TreeVertexes, because we will modify the network
      const vertexcoll = new go.Set(/*go.TreeVertex*/);
      vertexcoll.addAll(net.vertexes);
      for (const it = vertexcoll.iterator; it.next(); ) {
        const parent = it.value;
        // count the number of assistants
        let acount