public List<Node> build(){
??????? buildTree(root);
???????
??? }

??? private void buildTree(Node parent){
??????? Node node=null;
??????? Iterator<Node> it=nodes.iterator();
??????? while (it.hasNext()){
??????????? node=it.next();
??????????? if(Objects.equals(node.getParentId(),parent.getId())){
??????????????? parent.getChildren().add(node);
??????????? }
??????????? buildTree(node);
??????? }
??? }