Utilize the input text as a context reference, choose the right relationship between 'Syriza' and 'Alexis Tsipras' from the options.
Options: developer, chief executive officer, subsidiary, chairperson

Greek Prime Minister Alexis Tsipras was on Wednesday mulling whether to hold early elections after the austerity bailout split his radical left Syriza party, leaving him powerless to push further reform bills through parliament.
chairperson