Mayor Martin J. Walsh, the Boston Parks and Recreation Department, and The Friends of Copley Square welcome the holidays with the annual Copley Square Tree Lighting. The free event will feature appearances by Mayor Walsh, “Dining Playbook” host Jenny Johnson, Santa Claus, and Rudolph along with live entertainment including members of the Boston Pops Brass Ensemble, Berklee College of Music's co-ed contemporary a cappella group Pitch Slapped, “The Voice” contestant Brittany Butler, and a holiday sing-along. In addition, the US Postal Service will unveil its new holiday stamp.