Update tree in root to child manner on node click with recursion

I am working with Angular+ spring boot project, in which I have to show tree structure of my data as the data in in hierarchical manner.

public class TreeNode {

    private long nodeId;
    private String nodePath;
    private String hierarchyLevel;
    private String nodeFullPath;
    private Integer pageNumber;
    private String label;
    private Long parentNodeId;
    private List<OutlineNode> children = new LinkedList<>();

}

This is my TreeNode class for creating a node.
We have used mat-tree to create tree, for now the whole tree is created at once, so it takes long time to load the tree.
So I have to change the manner to generate tree as :

Tree example :

• root
  • child1
    • subchild1
      • a
        • a1
        • a2
      • b
    • subchild2
      • c
      • d
  • Child2
    • subchild3
      • f
      • j
    • subchild4

First need to load first level of tree :

• root
  • child1
  • child2

Then on click of the child1, I want to load its children nodes in the tree. The data of the nodes is fetched correctly, but I need to maintain a global variable for the tree to modify it as click on the node is performed. The request to load the tree come from Angular to Java so I need to maintain a tree to update it.

My issue is that I need to write many for loops as the tree get deeper. So I have written a recursive function, but it not working properly :

private TreeNode addChildren(TreeNode treeNodeOld, Long id) {
            for (TreeNode treeNode : treeNodeOld.getChildren()) {
                addChildren(treeNode, id);
                if (treeNode.getNodeId() == id) {
                    return treeNode;
                }
                addChildren(treeNode, id);
            }
            return null;
        } 

This method not working properly. I want to know the exact position to put child on it. The method wok fine for one level only, but as the tree grow deeper this is not working. I can work by writing for loop for each level, but this will increase lines of code and many time the level also will be unknown.

How can I update the tree in root to child manner without number of code by using recursion?

Change to something like:

private TreeNode addChildren(TreeNode treeNodeOld, Long id) {
            for (TreeNode treeNode : treeNodeOld.getChildren()) {
                if (treeNode.getNodeId() == id) {
                    return treeNode;
                }
                TreeNode found = addChildren(treeNode, id);
                if (found != null) {
                    return found;
                }
            }
            return null;
        }