well, You can add a menu item yourself. And you can call this menu item in the layout you are using.
Just place the whole menu item in a snippet and then call the whole snippen in the layout itself. You can add as many subitems as you want.
You can refer to the image below.
Hope it helps!
Hi Ananthapadmanabhan S
Go to Navigation document of your application and firstly add one item and select the particular item and click new subitem button on the menu list.
You can be able to add the navigation sub item.
if this information is not clear please elaborate your question for detailed explanation.
Try to generate overview pages for multiple sample entities which have 2 or 3 associations with each other, In the overview page you can get an idea of how its implemented, similar to what you have asked.
Right click on the module/folder ---> Add other ---> Menu (Create your navigation list here) ---> Add this Menu to snippet ---> Call this snippet in your layout.