Utilize the input text as a context reference, choose the right relationship between 'Syriza' and 'Alexis Tsipras' from the options.
Options: subsidiary, chairperson, manufacturer, legal form

ATHENS (Reuters) - Greek Prime Minister Alexis Tsipras contained a rebellion in his left-wing Syriza party to win parliamentary approval on Thursday for a second package of reforms required to start talks on a financial rescue deal.
chairperson