Add menu page with diffrent name from sub menu page in Wordpress

In wordpress if you are creating  a plugin the first sub menu page name is same as of plugin main menu page.
like if the name of plugin menu is Fund the by default the name of its first sub menu is also Fund.

To change this sub menu page you can make the slug for the submenu page equal that of the top level page.

add_action('admin_menu', 'my_plugin_menu');

function my_plugin_menu() {  
    add_menu_page('Page Title', 'Menu Title', 'manage_options', 'mymenu', 'display_menu);
    add_submenu_page('mymenu', 'sub_menu1 ', 'Sub menu name', 'manage_options','mymenu');
   add_submenu_page('mymenu', 'sub_menu2 ', 'Sub menu name2', 'manage_options','mymenu2');