The pilot reported that he had departed for a solo training flight to add a helicopter rating to his pilot certificate. He accelerated the helicopter to cruise flight and noticed an “unusual vibration.” He performed an immediate precautionary landing. During the touchdown sequence, one of the helicopter’s landing skids hit a tree branch, and the helicopter rolled onto its side. The helicopter’s main rotor impacted the tailboom, which separated from the fuselage. Several days after the accident, the pilot flew with his flight instructor in a different helicopter and attempted to replicate the vibration. As a result of this flight, the pilot believes that he encountered a tailwind during the accident flight that caused him to feel a vibration. Subsequently, the pilot reported no preimpact mechanical malfunctions or failures with the helicopter that would have precluded normal operation.