Analyze the relationship between 'Syriza' and 'Alexis Tsipras' within the context of the input sentence.
Options: parent organization, chairperson, creator, employer

Greek Prime Minister Alexis Tsipras tried to rally his Syriza party before a vote in parliament today (22 July) on the second package of measures demanded by international creditors to open talks on a new bailout deal.
chairperson