In many cases, tree or treegrid need to be built from multiple tables (each table represent separate level of tree/treegrid). For this purpose should be used TreeMultitableConnector/TreeGridMultitableConnector (instead of TreeConnector/TreeGridConector).

require("../../codebase/treemultitable_connector.php");
 
$tree = new TreeMultitableConnector($res);
$tree->setMaxLevel(3);
$level = $tree->get_level();
 
switch ($level) {
	case 0:
		$tree->render_table("projects2","project_id","project_name","","");
		break;
	case 1:
		$tree->render_sql("SELECT teams2.team_id, teams2.team_name, project_team2.project_id FROM teams2 INNER JOIN project_team2 ON teams2.team_id=project_team2.team_id", "team_id", "team_name", "", "project_id");
		break;
	case 2:
		$tree->render_table("developers2", "developer_id", "developer_name", "", "developer_team");
		break;
	case 3:
		$tree->render_table("phones2", "phone_id", "phone", "", "phone_developer");
		break;
}

require("../../codebase/treegridmultitable_connector.php");
 
$treegrid = new TreeGridMultitableConnector($res);
$treegrid->setMaxLevel(3);
$level = $treegrid->get_level();
...