Complex sentence: McGrath announced his retirement from Test cricket on 23 December 2006, with his Test career coming to an end after the fifth Ashes test in Sydney in January 2007, whilst the 2007 World Cup marked the end of his one-day career.
Split into simpler sentences: McGrath announced his retirement from Test cricket on 23 December 2006. His Test career came to an end after the 5th Ashes test in Sydney, whilst the 2007 World Cup marked the end of his one-day career.