如何深度复制二叉树？

尝试

class Node {    private String value;    private Node left;    private Node right;    public Node(String value, Node left, Node right) {        this.value = value;        ...    }    Node copy() {        Node left = null;        Node right = null;        if (this.left != null) { left = this.left.copy();        }        if (this.right != null) { right = this.right.copy();        }        return new Node(value, left, right);    }}