如何在二叉树中返回用于顺序遍历的迭代器？

import java.util.Stack;

public class BinaryTreeIterator {
    private Stack<TreeNode> stack;

    public BinaryTreeIterator(TreeNode root) {
        stack = new Stack<>();
        if (root != null) {
            stack.push(root);
            pushLeftNodes(root.left);
        }
    }

    public boolean hasNext() {
        return !stack.isEmpty();
    }

    public int next() {
        TreeNode node = stack.pop();
        if (node.right != null) {
            stack.push(node.right);
            pushLeftNodes(node.right.left);
        }
        return node.val;
    }

    private void pushLeftNodes(TreeNode node) {
        while (node != null) {
            stack.push(node);
            node = node.left;
        }
    }

    public void remove() {
        // 实现删除当前节点的逻辑
    }
}