Greentree is a 400-acre (1.6 km2) estate in Manhasset, New York on Long Island. Payne Whitney purchased the estate for his bride, Helen Julia Hay, in 1904. Later, John Hay Whitney and his second wife, Betsey, occupied the main house, where Mrs. Whitney remained in residence there until her death in 1998.
Radio and TV talk show pioneers John Reagan "Tex" McCrary, and his wife, model and movie star Jinx Falkenburg, intermittently lived on the Jock Whitney estate with their sons from 1947 to 1977.
As with other Gold Coast Mansions, the original estate was pieced together. The five family farms that were purchased to make up the new estate were the Mitchell, Ketchum, Brinkerhoff, Skidmore, and Schenck farms. The estate was later divided, with gifts of land being made to several organizations. The North Shore Unitarian Universalist Society, now known as the Unitarian Universalist Congregation at Shelter Rock (UUCSR), received a portion adjacent to Shelter Rock Road and has built a large Worship Hall on the site of the former Apple Orchard. The old clay real tennis court was removed at that time. North Shore Manhasset Hospital also received a donation of property adjacent to Community Drive. John Hay Whitney was an honorary member of the Manhasset Lakeville Fire Department, and donated the land along Community Drive East to be the site of the M.L.FD. Company Two fire house, and Nassau County Police Departments 6th Precinct. The remaining 408 acres, including the family home, are run by the Greentree Foundation, as a conference center dedicated to international justice and human rights issues.
The estate has hosted the Manhasset negotiations, a round of talks between Morocco and the Polisario Front, August 10–12, 2007, as part of a set of UN-led meetings centering on the future of Western Sahara, among others.