code: function nextAncestor(nodeInLeft, node, ancestor) {
      return nodeInLeft.hierNode.ancestor.parentNode === node.parentNode
          ? nodeInLeft.hierNode.ancestor : ancestor;
  }
docs: If nodeInLeft’s ancestor is a sibling of node, returns nodeInLeft’s ancestor.
  Otherwise, returns the specified ancestor.
  
  @param  {module:echarts/data/Tree~TreeNode} nodeInLeft
  @param  {module:echarts/data/Tree~TreeNode} node
  @param  {module:echarts/data/Tree~TreeNode} ancestor
  @return {module:echarts/data/Tree~TreeNode}