Locally store books from server and show users on swift/iOS App in list view(5 nested list/webview)

Need to upgrade an existing book app from 2 level nested list with sub chapter to level 5 nested list for database . when server uploads the new book , user need to save it locally and read in app later whenever needed from notification. The given screenshot is an example of a level 2 nested list. We want to add json format books with sub chapters upto 5 level nested list.