Arthur Ronald Lambert Field Tree (26 September 1897 – 14 July 1976) was a British Conservative Party politician, journalist and investor who served as the Member of Parliament (MP) for the Harborough constituency in Leicestershire from 1933 to 1945. He later established the Sandy Lane resort in Barbados.
Tree's father, Arthur Tree, was an English real estate developer and son of Lambert Tree, a former British minister to Russia. His mother, Ethel Field, was a daughter of Marshall Field, a co-founder of Marshall Field's department store in Chicago, Illinois. Born in the United States, he was educated at Winchester College in England. Two months after his parents' divorced in 1901, Tree's mother married her lover, Capt. David Beatty, the future 1st Earl Beatty and First Sea Lord. His half-siblings were David Beatty, 2nd Earl Beatty, and the Hon Peter Beatty; he also had two full siblings, both of whom died in infancy.
Tree edited Forum Magazine in New York from 1922, and in 1926 became involved in investment on the , before the Wall Street Crash of 1929.
Tree returned to England with his wife, the former Nancy Keene Perkins (the widow of his cousin Henry Marshall Field) in 1927, where they had two sons, one of them racehorse trainer Jeremy Tree, and a daughter, who died at birth. At first the couple took a 10-year repairing lease on Kelmarsh Hall near Market Harborough, Northamptonshire which Nancy redecorated with help from Mrs Guy Bethell of Elden Ltd.