How to hide plugin submenu title in drop down in admin panel in wordpress?

I have created a plugin that has some sub menus i.e add new list, besides that I also have pages to update the data, But I don't want to display these sub menus in dropdown. Here is my code.

add_submenu_page(
testimonial,
Manage Testimonial,
Manage Testimonial,
manage_options,
manage-testimonial,
manage_testimonial

);

add_submenu_page(
testimonial,
null,
null,
manage_options,
edit-testimonial,
edit_testimonial

);

If I use this it adds blank ul for these, How can I do this. This is the admin panel drop down.