Return ``True`` if this page is the first root pages.

def is_first_root(self):
        """Return ``True`` if this page is the first root pages."""
        if self.parent:
            return False
        if self._is_first_root is not None:
            return self._is_first_root
        first_root_id = cache.get('PAGE_FIRST_ROOT_ID')
        if first_root_id is not None:
            self._is_first_root = first_root_id == self.id
            return self._is_first_root
        try:
            first_root_id = Page.objects.root().values('id')[0]['id']
        except IndexError:
            first_root_id = None
        if first_root_id is not None:
            cache.set('PAGE_FIRST_ROOT_ID', first_root_id)
        self._is_first_root = self.id == first_root_id
        return self._is_first_root