def train(self, sentences, model):
        """Train the CRF tagger using CRFSuite.

        :params sentences: Annotated sentences.
        :params model: Path to save pickled model.
        """
        trainer = pycrfsuite.Trainer(verbose=True)
        trainer.set_params(self.params)
        for sentence in sentences:
            tokens, labels = zip(*sentence)
            features = [self._get_features(tokens, i) for i in range(len(tokens))]
            trainer.append(features, labels)
        trainer.train(model)
        self.load(model)