What is the relationship between 'St George Bank' and 'Westpac' in the context of the input sentence.
Options: parent organization, position held, stock exchange, location of formation

Mrs Kelly was chief executive and managing director of St George Bank from 2002 to 2007 and CEO of Westpac from 2008 until early this year, overseeing a merger of the two banks in 2008.
parent organization