Hi Krishna Vamshi,

                 You mentioned like“ I have a requirement where in navigation I need to have a parent page and have multiple child pages that pop when clicked on the parent page navigation “. From my understanding, Parent page and child age which means Navigation list and their sub lists you are trying to convey. Right ?. If it is right, It may be the answer for your doubt. if its wrong,  Kindly let me know.  We can able to create Sub lists under one parent list. You can able to navigate to different page if the parent list don’t have any Sub list item. But we can’t specify on click action on the parent list which has Sub lists.

You can clearly see, I try to create Parent list with On click action. It throws error. Because, I have Sub item (Test) for this parent (Home) item. If you want the navigation tree in left side, create pages with Atlas_Default_Sidebar Layout. Whatever pages created with this Sidebar layout, Navigation tree will come at left side. 

Edited :    Create one navigation tree, In this navigation tree, you can create the same Menu item and Sub menu items. When you double click on the Default Navigation tree which is located in left side of the scroll containers, you will get the option to Map this Navigation tree. Select Menu Document option and map this Menu navigation tree. For your reference, I duplicated the Atlas_Default layout and Mapped the Menu document in this layout.