Organizers for this year’s Festival of Trees, which will mark its 20th anniversary, are inviting the community to participate in a fund-raiser to support the event. The inaugural Emerald City Treasure Hunt begins on Sunday and will run until Dec. 1. Players can register for $10, then search for special emerald medallions displayed at historic preservation sites throughout the Merrimack Valley. By correctly recording the numbers on the medallions, players are then entered to win a trip for two to Ireland. The Festival of Trees , running Nov. 23 to Dec. 7, raises funds to preserve heritage and historical monuments throughout the Merrimack Valley. For more information or to register for the hunt, visit www.methuenfestivaloftrees.com.