```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="validation")
        >>> new_review = {'label': 0, 'text': 'this movie is the absolute worst thing I have ever seen'}
        >>> ds = ds.add_item(new_review)
        >>> ds[-1]
        {'label': 0, 'text': 'this movie is the absolute worst thing I have ever seen'}
        ```
        """
        item_table = InMemoryTable.from_pydict({k: [v] for k, v in item.items()})
        # We don't call _check_if_features_can_be_aligned here so this cast is "unsafe"
        dset_features, item_features = _align_features(
            [self._info.features, Features.from_arrow_schema(item_table.schema)]
        )
        # Cast to align the schemas of the tables and concatenate the tables
        table = concat_tables(
            [
                self._data.cast(dset_features.arrow_schema) if self._info.features != dset_features else self._data,
                item_table.cast(item_features.arrow_schema),