code: def commitTxns(self, count: int) -> Tuple[Tuple[int, int], List]:
          
          committedSize = self.size
          committedTxns = []
          for txn in self.uncommittedTxns[:count]:
              txn.update(self.append(txn))
              committedTxns.append(txn)
          self.uncommittedTxns = self.uncommittedTxns[count:]
          logger.debug('Committed {} txns, {} are uncommitted'.
                       format(len(committedTxns), len(self.uncommittedTxns)))
          if not self.uncommittedTxns:
              self.uncommittedTree = None
              self.uncommittedRootHash = None
          # Do not change `uncommittedTree` or `uncommittedRootHash`
          # if there are any `uncommittedTxns` since the ledger still has a
          # valid uncommittedTree and a valid root hash which are
          # different from the committed ones
          if committedTxns:
              return (committedSize + 1, committedSize + count), committedTxns
          else:
              return (committedSize, committedSize), committedTxns
docs: The number of txns from the beginning of `uncommittedTxns` to commit
          :param count:
          :return: a tuple of 2 seqNos indicating the start and end of sequence
          numbers of the committed txns