Dashboard Menu settings

Try this code:

add_action('admin_menu', 'custom_menu_page');
function custom_menu_page(){
add_menu_page( 'Pages', 'Pages', 'manage_options', 'Pages', 'page_callback_function', 'dashicons-media-spreadsheet', 26 );
add_submenu_page( 'Pages', 'All Pages', 'All Pages', 'manage_options', 'all-pages-list', 'subpage_callback_function' ); 
}