inserting in binary tree doesn't work using java

I'm currently learning about trees using java and i have some errors going on here in the insertion of items in a binary tree I don't why it doesn't work

this is the code: tree node:

public class TNode {
    int data;
    TNode left;
    TNode right;

    public TNode(int data) {
        this.data = data;
        left = null;
        right = null;
    }
}

tree class:

public class Tree {
    TNode root;

    public Tree(){
        root = null;
    }

    public TNode insertNode(TNode item, int d) {
        if (item == null) {
            return new TNode(d);
        }

         if (d < item.data) {
            item.left = insertNode(item, d);
        }

        if (d > item.data) {
            item.right = insertNode(item, d);
        } else {
            return item;
        }

        return item;
    }

    public void add(int d) {
        insertNode(root, d);
    }
}

Whenever I add an item the root remains null with no right or left items if someone can help I'll be really thankful

root is always null because you never assign value to it.

you can add to the beginning of your method check and assign it

public TNode insertNode(TNode item, int d){
    if(item == null){
        TNode node = new TNode(d);
        if (root == null) { 
            root = node;
        }
        return node
    }
    ... rest of method isn't changed...

Also when you are recursing you should make a call with a proper child node instead of always calling with item, so for example first case would be:

    item.left = insertNode(item.left, d);

For second case you would just use item.right instead.