_findCommonParent(childA, childB) {
    const parents = {};
    const iterateParents = (parents, child) => {
      const parentRef = this.hierarchical.parentReference[child];
      if (parentRef !== undefined) {
        for (let i = 0; i < parentRef.length; i++) {
          const parent = parentRef[i];
          parents[parent] = true;
          iterateParents(parents, parent);
        }
      }
    };
    const findParent = (parents, child) => {
      const parentRef = this.hierarchical.parentReference[child];
      if (parentRef !== undefined) {
        for (let i = 0; i < parentRef.length; i++) {
          const parent = parentRef[i];
          if (parents[parent] !== undefined) {
            return { foundParent: parent, withChild: child };
          }
          const branch = findParent(parents, parent);
          if (branch.foundParent !== null) {
            return branch;
          }
        }
      }
      return { foundParent: null, withChild: child };
    };

    iterateParents(parents, childA);
    return findParent(parents, childB);
  }
Find a common parent between branches.
@param {Node.id} childA
@param {Node.id} childB
@returns {{foundParent, withChild}}
@private