THE NON-INSTRUMENT RATED PILOT RECEIVED A WEATHER BRIEFING VIA A NATIONAL WEATHER SERVICE RADIO BROADCAST AND HE THEN DEPARTED ON A POSITIONING FLIGHT. EN ROUTE HE ENCOUNTERED DETERIORATING WEATHER CONDITIONS. WHILE MANEUVERING TO RETURN TO HIS DEPARTURE POINT, HE INADVERTENTLY ENTERED A CLOUD AND STRUCK TREES PRIOR TO REGAINING VISUAL METEOROLOGICAL CONDITIONS.