Green Tree was named for a large sycamore tree along Greentree Road where the stagecoaches would deliver mail. It was a place to meet in the community. The borough's logo is a drawing of the original Green Tree.
Green Tree was known by many other names before it became Green Tree, such as Peters Township of Allegheny County (1781-1788), St. Clair Township of Allegheny County (1788-1805), Lower St. Clair (1805-1851), Chartiers (1851-1860), Kirkpatrick (1860-1861), and Union (1861-1885). It became Green Tree in 1885.
Green Tree was once part of the state of Virginia.
The Green Tree Public Library was started in the 1940's at the urging of the literacy group of the Green Tree Woman's Club and staffed entirely by volunteers.
The Green Tree Police Department was started in 1908 with one part-time officer.
In the early 20th century, Green Tree grew as a result of the Wabash Railroad that built Rook Station.
Since incorporated in 1885, Green Tree has always had a local school (School Street School, Manilla Avenue School, and Aiken Elementary).
George Washington traveled Greentree Road using the Native American trail in search of a more direct route between Fort Pitt and Fort Henry in West Virginia.