simplification of function signature in Java

Question

I want to "simplify" the signature of functions, but I'm not sure if this action is possible. If anyone can help me I will be very grateful.

Could anyone help me how to transfer the code from this:

(In the main Main class I wrote the lines below)

Tree tree = new Tree(15);

        int[] set1 = {15, 21, 8, 41, 8, 5, 41, 33};
        int[] set2 = {18, 45, 36, 19, 3, 24, 19, 10};

        for (int i = 0; i < set1.length; i++) {
            tree.add(tree, set1[i]);
        }

        System.out.println("The depth of the tree is " + tree.depth(tree) + ".");

I want to remove the input (Tree tree) for the functions of the Tree class, if this action is possible:

Tree tree = new Tree(15);

        int[] set1 = {15, 21, 8, 41, 8, 5, 41, 33};
        int[] set2 = {18, 45, 36, 19, 3, 24, 19, 10};

        for (int i = 0; i < set1.length; i++) {
            tree.add(set1[i]);
        }

        System.out.println("The depth of the tree is " + tree.depth() + ".");

Tree class:

public class Tree {

    /**
     * The value of this node in the tree.
     */
    public int node;

    /**
     * The left subtree.
     */
    private Tree lhs;

    /**
     * The right subtree.
     */
    private Tree rhs;

    /**
     * Creates a new tree with the value node.
     * @param node The value of this node in the tree.
     */
    public Tree(int node) {
        this.node = node;
        this.lhs = null;
        this.rhs = null;

    }

 public void add(Tree tree, int insert) {
        addRecursive(tree, insert);
    }

    private Tree addRecursive(Tree current, int value) {
        if (current == null) {
            return new Tree(value);
        }

        if (value < current.node) {
            current.lhs = addRecursive(current.lhs, value);
        } else if (value > current.node) {
            current.rhs = addRecursive(current.rhs, value);
        } else {
            // value already exists
            return current;
        }

        return current;
    }

public int depth(Tree tree) {
        // Root being null means tree doesn't exist.
        if (tree == null)
            return 0;

        // Get the depth of the left and right subtree
        // using recursion.
        int leftDepth = depth(tree.lhs);
        int rightDepth = depth(tree.rhs);

        // Choose the larger one and add the root to it.
        if (leftDepth > rightDepth)
            return (leftDepth + 1);
        else
            return (rightDepth + 1);
    }

}