BackTerminal.frmCatMan.InitializeTreeViewCategory C# (CSharp) Method

        private void InitializeTreeViewCategory()
        {
            SqlConnection connection = Library.Connection.Instance();
            string queryString = "SELECT * FROM dbo.category ORDER BY parent_id, title;";
            SqlCommand command = new SqlCommand(queryString, connection);
            SqlDataReader reader = command.ExecuteReader();

            tvCategory.Nodes.Add(root);

            while (reader.Read())
            {
                Category cat;
                cat.id = (int)reader["id"];
                cat.title = (String)reader["title"];
                cat.parent_id = 0;
                if (!(reader["parent_id"] is DBNull))
                    cat.parent_id = (int)reader["parent_id"];
                if (cat.parent_id == 0)
                {
                    tvCategory.Nodes[0].Nodes.Add(cat.id.ToString(), cat.title);
                }
                else
                {
                    NodeFromKey(cat.parent_id.ToString()).Nodes.Add(cat.id.ToString(), cat.title);
                }
                Console.Out.WriteLine(cat.title);
            }
            reader.Close();
            tvCategory.ExpandAll();
        }