If you look at the browser’s address bar on that page’s edit screen, you see something like this:
wp-admin/post.php?post=91&action=edit
The 91 is the post id. This is the important information, you can create a sub menu page for that now.
To add a page to the the admin menu, use the hook admin_menu and the function add_submenu_page(). Set the page menu as parent and the URL of the Camp page as menu URL:
add_action( 'admin_menu', function() {
add_submenu_page(
'edit.php?post_type=page',
'Camp',
'Camp',
'edit_pages',
'post.php?post=91&action=edit'
);
});
That’s all. 🙂