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);
        }
    }