def _latest_feature_bucket(changelog):
    """
    Select 'latest'/'highest' unreleased feature bucket from changelog.

    :returns: a string key from ``changelog``.
    """
    unreleased = [x for x in changelog if x.startswith("unreleased_")]
    return sorted(
        unreleased, key=lambda x: int(x.split("_")[1]), reverse=True
    )[0]