Noun
three-on-the-tree (plural three-on-the-trees)
(US, idiomatic) On an automobile (especially those produced from 1939 through the mid-1970s), a three-speed manual transmission whose gearshift lever is mounted on the steering column.
In driver's education, they used to teach students to drive in cars with a three-on-the-tree, but now the cars all have automatic transmission.