def previous(options = {})
      pages = self_and_siblings.where('lft < ?', lft)
      select_page(pages, options.merge(order: :desc))
    end
def previous(options = {})
      pages = self_and_siblings.where('lft < ?', lft)
      select_page(pages, options.merge(order: :desc))
    end
Returns the previous page on the same level or nil.

 @option options [Boolean] :restricted (false)
   only restricted pages (true), skip restricted pages (false)
 @option options [Boolean] :public (true)
   only public pages (true), skip public pages (false)