With the passengers on board, the pilot took off to a hover and air taxied his aircraft backwards in order to maximise the length of his take off run. During this manoeuvre the four main rotors struck near the top of a large conifer tree, approximately 15 feet high. The tail rotor was undamaged as it went abeam the tree and did not touch it. The pilot, who felt vibrations through his controls, landed immediately and shut down the aircraft. Both he and his passengers exited the aircraft without delay. The pilot said that he did not see the tree which was to the left rear of his aircraft. He occupied the right hand seat.