public Form3()
        {
            InitializeComponent();

            TreeNode t1 = new TreeNode("中国");

            TreeNode t2 = new TreeNode("北京");

            TreeNode t3 = new TreeNode("朝阳区");

            t2.Nodes.Add(t3);

            t1.Nodes.Add(t2);

            treeView1.Nodes.Add(t1);
        }

public partial class Form3 : Form
    {
        List<China> alllist = new List<China>();

        public Form3()
        {
            InitializeComponent();

            alllist = new ChinaData().Select();

            TreeNode tn1 = new TreeNode("中国");
            tn1.Tag = "0001";

            NodesBind(tn1);

            treeView1.Nodes.Add(tn1);
            
        }

        public void NodesBind(TreeNode tn)
        {
            List<China> clist = alllist.Where(r => r.ParentAreaCode == tn.Tag.ToString()).ToList();

            foreach (China c in clist)
            {
                TreeNode tnn = new TreeNode(c.AreaName);
                tnn.Tag = c.AreaCode;

                //递归
                NodesBind(tnn);

                tn.Nodes.Add(tnn);
            }
        }

    }