Prior to a flight from Charleston, WV to Sault Ste Marie, MI, the pilot was briefed to expect icing conditions. During the flight, mixed and rime icing conditions were encountered; however, the deicing equipment removed it satisfactorily. An update weather briefing was not obtained for a return flight. After takeoff, the pilot leveled at 7000 ft MSL. About 22 min later, he requested a lower altitude because of heavy icing conditions. The aircraft was clear to 6000 ft, then 5000 ft, but was still in icing conditions. A climb to 9000 was then unsuccessfully attempted. The pilot then diverted toward Gaylord and was cleared to 3500 ft. The pilot saw the airport while at an altitude of about 900 ft AGL, but was unable to maneuver the plane to land on a runway. Finally, at an altitude of about 50 ft AGL, he leveled the wings and landed straight ahead. During the landing roll-out, the aircraft collided with trees.