Args:
            tree (dict): Tree history of all editions of a piece.
            edition_number (int): The edition number to check for.
                In the case of a piece (master edition), an empty
                string (``''``) or zero (``0``) can be passed.

        Returns:
            list: The chain of ownsership of a particular
            edition of the piece ordered by time.

def chain(tree, edition_number):
        """
        Args:
            tree (dict): Tree history of all editions of a piece.
            edition_number (int): The edition number to check for.
                In the case of a piece (master edition), an empty
                string (``''``) or zero (``0``) can be passed.

        Returns:
            list: The chain of ownsership of a particular
            edition of the piece ordered by time.

        """
        # return the chain for an edition_number sorted by the timestamp
        return sorted(tree.get(edition_number, []), key=lambda d: d['timestamp_utc'])