Complex sentence: Unveiled by the Queen and the Duke of Edinburgh who planted a flowering cherry tree during a commemorative ceremony is a plaque that reads: This tree was planted by Her Majesty Queen Elizabeth on May 9th 1997.
Split into simpler sentences: Unveiled by the Queen and the Duke of Edinburgh who visited and planted a flowering cherry tree during a commemorative ceremony. The commemorative plaque reads: This tree was planted by Her Majesty Queen Elizabeth on May 9th 1997.