Solution:
Use following code
//Main admin menus
add_action('admin_menu', 'add_my_custom_menu');
function add_my_custom_menu() {
//add an item to the menu
add_menu_page(
'My Plugin',
'My Plugin',
10,
plugin_dir_path(__FILE__).
'admin/plugin-form.php',
'',
plugin_dir_url(__FILE__).
'img/contact.png'
);
add_submenu_page(
'my-plugin-name/admin/plugin-form.php',
'Plugin Setting',
'Plugin Setting',
10,
plugin_dir_path(__FILE__).
'admin/plugin-form.php',
'myplugin_options_page'
);
add_submenu_page(
'my-plugin-name/admin/plugin-form.php',
'Plugin Entries',
'Plugin Entries',
10,
plugin_dir_path(__FILE__).
'admin/entries.php',
''
);
}
reason is that every first sub-menu’s destination page/function will be the same as main menu destination.