The electricity for the lights was cut as police and firefighters responded around noon Wednesday after Noel Delgado climbed the tree on the New Haven Green, a 16-acre park in downtown New Haven near Yale University.
Delgado had two banners in the tree. Police Lt. Jeff Hoffman said he shouted about various causes.
Officers talked with Delgado and persuaded him to climb down.
Delgado has been charged with breach of peace. Police say he refused medical treatment.
There's no telephone number listed for Delgado at his New Haven address.