节点的增加，删除，修改

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Tree
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
      
        private void button1_Click(object sender, EventArgs e)
        {
            string type = textBox1.Text.Trim();
            TreeNode rootNode;
            rootNode = this.treeView1.Nodes.Add(type);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if(this.textBox1.Text!=string.Empty){
                string type = textBox1.Text.Trim();
                treeView1.SelectedNode.Nodes.Add(type);
                treeView1.ExpandAll();
            }

          
        }

        private void 删除ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            TreeNode type = treeView1.SelectedNode;
            type.Remove();
        }

        private void 修改ToolStripMenuItem_Click(object sender, EventArgs e)
        {
          
            if(this.treeView1.SelectedNode!=null){
                treeView1.SelectedNode.Text = textBox1.Text;
                if(this.treeView1.SelectedNode.Text!=null&&this.treeView1.Nodes.Count==0){
                    TreeNode type = new TreeNode();
                    treeView1.ExpandAll();
                }
            }
        }

        private void button3_Click(object sender, EventArgs e)
        {
           
          
            }
       
    }
}