The original drag-racing Christmas Tree had five amber lights on each side. It debuted at the 1963 U.S. Nationals at Indianapolis Raceway Park, using the amber bulbs as a sequential countdown before green.
That first design did not include the modern pre-stage and stage indicators. Those small bulbs were added for the 1964 Winternationals, and the staging lights were gradually moved from the track onto the Tree.
A common mix-up comes from later versions. In 1986, the NHRA removed two amber bulbs from each side, leaving three large amber countdown lights. Modern trees also use blue staging lights, but those features were not part of the original five-amber-light arrangement.