public void ShowBook()
        {
            string connStr = "Server=.;Database=Book;UID=sa;pwd=sasa";
            string sql = "select * from BookType";
            SqlConnection connection = new SqlConnection(connStr);
            SqlCommand command = new SqlCommand(sql, connection);
            try
            {
                connection.Open();
                SqlDataReader reader = command.ExecuteReader();
                while (reader.Read())
                {
                    TreeNode typeNode=new TreeNode(reader["TypeName"].ToString());
                    int typeId=Convert.ToInt32(reader["TypeId"]);
                    sql = string.Format("select BookId,BookName from Books where BookType={0}", typeId);
                    SqlConnection bookConn = new SqlConnection(connStr);
                    command = new SqlCommand(sql, bookConn);
                    bookConn.Open();
                    SqlDataReader bookReader = command.ExecuteReader();

                    while (bookReader.Read())
                    {
                        TreeNode bookNode = new TreeNode(bookReader["BookName"].ToString());
                        bookNode.Tag = bookReader["BookId"];
                        typeNode.Nodes.Add(bookNode);
                    }
                    bookReader.Close();
                    bookConn.Close();
                    this.tvwBook.Nodes[0].Nodes.Add(typeNode);
                }
                reader.Close();
                connection.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
                connection.Close();
            }
        }

提示：指定的参数已超出有效值的范围。参数名：index

this.tvwBook.Nodes[0].Nodes.Add(typeNode);这一句表示你在tvwBook的第一个节点下，增加一个typeNode子节点，可是目前你的tvwBook下连一个节点都还没有。你首先要增加一个节点，才能在这个节点下增加子节点