Analyze the relationship between 'Syriza' and 'Alexis Tsipras' within the context of the input sentence.
Options: member of, chairperson, subsidiary, distributed by

Greek Prime Minister Alexis Tsipras is trying to turn a corner after he reluctantly agreed to negotiate a third bailout, allowing the European Central Bank to top up bank credit lines but prompting a rebellion in his leftist Syriza party.
chairperson