The helicopter collided with a tree during a landing after a decay in rotor RPM during takeoff. According to the pilot, the aircraft was facing southeast prior to departure and the pilot estimated that the wind was from the northwest at 8 kts. Following a pedal turn into the wind after takeoff, maximum performance was executed to clear a tree that was 10 ft higher than the saddle between 2 ridges where the takeoff took place. Near the top of the tree, there was a rapid decay of rotor RPM. Due to terrain considerations, the pilot chose not to lower collective. The aircraft was flying near a steep slope, so the pilot elected to land in the oak tree to prevent a downhill roll. He did not flare to prevent ballooning over the tree. The aircraft was about 12 lbs. under max gross weight. Density altitude was about 2000 ft. During the landing, the aircraft was substantially damaged. The 3 occupants received minor injuries.