_generateMap() {
    const fillInRelations = (parentNode, childNode) => {
      if (
        this.hierarchical.levels[childNode.id] >
        this.hierarchical.levels[parentNode.id]
      ) {
        this.hierarchical.addRelation(parentNode.id, childNode.id);
      }
    };

    this._crawlNetwork(fillInRelations);
    this.hierarchical.checkIfTree();
  }
Update the bookkeeping of parent and child.
@private