public class Class1 : TreeNode
    {
 
        public static int cnt = 0;
        public Class1()
        {
            cnt++;
            Console.WriteLine("begin of Class1");
        }
        ~Class1()
        {
            cnt--;
            Console.WriteLine("end of Class1");
        }
    }

 
        private void Button2_Click(object sender, EventArgs e)
        {
            TreeNode t = new Class1();
            t.Text = "Root";
            treeView1.Nodes.Add(t);
        }
 
        private void Button4_Click(object sender, EventArgs e)
        {
            treeView1.Nodes.Clear();
            GC.Collect();
            GC.WaitForPendingFinalizers();
            GC.Collect();
            Console.WriteLine("Number of Class1 instances " + Class1.cnt);
        }