add a menu item

add to theme’s functions.php
(or add as a plugin to your /wp-content/mu-plugins/)

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

function toolbar_link_to_mypage( $wp_admin_bar ) {
	$args = array(
		'id'    => 'my_page',
		'title' => 'My Page',
		'href'  => 'http://mysite.com/my-page/',
		'meta'  => array( 'class' => 'my-toolbar-page' )
	);
	$wp_admin_bar->add_node( $args );
}

https://codex.wordpress.org/Class_Reference/WP_Admin_Bar/add_node
http://codex.wordpress.org/Must_Use_Plugins