The pilot reported that he departed on an instrument flight rules flight plan into a low overcast cloud ceiling. He commented that he lost visual contact with the ground immediately upon liftoff. During the initial climb, the airplane momentarily entered a nose-down attitude. He subsequently corrected the nose down attitude. However, as the airplane began to climb again the right wing impacted a tree. This occurred approximately 1 mile from the airport and within 1 minute of takeoff. After the in-flight collision, he had "full function" of the airplane and elected to continue the planned 31-minute flight to the intended destination. He added that there were no anomalies related to flight control or engine operation during the flight. A post accident inspection revealed impact damage to the leading edge of the right wing, right engine nacelle, and right propeller spinner. In addition, the inspection revealed a 3-inch crack in the aft wing spar at the right main landing gear wheel well.