Insert some new pairs, and keep the _key_ids updated.
        
        Params:
            ids_and_pairs -- A list of (index, (key, value)) tuples.

def _insert_pairs(self, ids_and_pairs):
        """Insert some new pairs, and keep the _key_ids updated.
        
        Params:
            ids_and_pairs -- A list of (index, (key, value)) tuples.
        
        """
        ids_to_insert = [x[0] for x in ids_and_pairs]
        
        # We use the bisect to tell us how many spots the given index is
        # shifting up in the list.
        for ids in self._key_ids.itervalues():
            for i, id in enumerate(ids):
                ids[i] += bisect(ids_to_insert, id)
        
        # Do the actual insertion
        for i, pair in ids_and_pairs:
            self._pairs.insert(i, pair)