Into the very early years of the 20th century people actually burned CANDLES on their Christmas tree! Seems crazy now but without electricity, candles or oil lamps were the only lighting options for displaying a holiday tree in the evening for most. A drying, combustible Christmas tree is an extreme fire hazard and the obvious result of a close flame caused many a horrible holiday season for candle users.
An associate and friend of Thomas Edison, Edward Johnson, is recognized as the first person to put electrified lights on a real Christmas tree. It happened in 1882 and just three years after the incandescent light bulb was invented. Johnson was a New Yorker and an executive of the Edison Illumination Company of New York City.
Here is a short history of the first Christmas tree illuminated with electric lights.