This is a sample child page for the Parent page item SubPages.
The sidebar menu is automatically generated when creating a menu item with the same name as the parent page.
Since this page is called 'SubPages' we create a Menu item named "SubPages" as well.
Then set the menu item type to a StaticPage, and ensure "Allow nested items" and "Replace this item with its generated children" are selected.
The Sidebar Menu should then be automatically generated when visiting any of the child pages.