From Access Db to Treeview

string strProvider = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=axb.mdb";
            string strSql = "SELECT Categories , subcategories FROM Categories INNER JOIN subcategories ON Categories .Key= subcategories.Id";
            OleDbConnection con = new OleDbConnection(strProvider);
            OleDbCommand cmd = new OleDbCommand(strSql, con);
            con.Open();
            cmd.CommandType = CommandType.Text;
            OleDbDataReader dr = cmd.ExecuteReader();
 
             DataTable dtTree = new DataTable();
 
             int columnCount = dr.FieldCount;
 
             for (int i = 0; i < columnCount; i++)
             {
                 dataGridView1.Columns.Add(dr.GetName(i).ToString(), dr.GetName(i).ToString());
             }
 
 
             string[] rowData = new string[columnCount];
             while (dr.Read())
             {
                 for (int k = 0; k < columnCount; k++)
                 {
                     if (dr.GetFieldType(k).ToString() == "System.Int32")
                     {
                         rowData[k] = dr.GetInt32(k).ToString();
                     }
 
                     if (dr.GetFieldType(k).ToString() == "System.String")
                     {
                         rowData[k] = dr.GetString(k);
                     }
                 }
 
                 dataGridView1.Rows.Add(rowData);
             }