Page URL and Custom Menu structure with Main Pages

I have 4 Pages, all are Main page i.e. no parent.

• Menu Item A
• Menu Item B
• Menu Item C
• Sub Menu 1

Now, I have created the given menu from Appearance >> Menus

Menu Item A
Sub Menu 1

Menu Item B
Sub Menu 1

Menu Item C
Sub Menu 1

But when I click in “Sub Menu 1” under “Menu Item A“, the URL shows

https://www.domain.com/sub-menu-1

again when I click in “Sub Menu 1” under “Menu Item B“, the URL shows

https://www.domain.com/sub-menu-1

Rather I want them to show as mentioned below…

https://www.domain.com/menu-item-a/sub-menu-1

https://www.domain.com/menu-item-b/sub-menu-1

Any, suggestion how to achieve this other than creating 3 clone child pages of “sub-menu-1” for all the root menu items.