add_action( 'admin_bar_menu', 'add_nodes_and_groups_to_toolbar', 999 );

function add_nodes_and_groups_to_toolbar( $wp_admin_bar ) {

	// add a parent item
	$args = array(
		'id'    => 'parent_node',
		'title' => 'parent node'
	);
	$wp_admin_bar->add_node( $args );

	// add a child item to our parent item
	$args = array(
		'id'     => 'child_node',
		'title'  => 'child node',
		'parent' => 'parent_node'
	);
	$wp_admin_bar->add_node( $args );

	// add a group node with a class "first-toolbar-group"
	$args = array(
		'id'     => 'first_group',
		'parent' => 'parent_node',
		'meta'   => array( 'class' => 'first-toolbar-group' )
	);
	$wp_admin_bar->add_group( $args );

	// add an item to our group item
	$args = array(
		'id'     => 'first_grouped_node',
		'title'  => 'first group node',
		'parent' => 'first_group'
	);
	$wp_admin_bar->add_node( $args );

	// add another child item to our parent item (not to our first group)
	$args = array(
		'id'     => 'another_child_node',
		'title'  => 'another child node',
		'parent' => 'parent_node'
	);
	$wp_admin_bar->add_node( $args );

}