Like so many American traditions, the Christmas tree emerged from the hearty jumble of 19th-century immigrant custom and religious observance, spun up in the post-Civil War national rebuilding project, and became industrialized and commercialized in the great acceleration of modern times.
From its 1840s incarnation as a small plant placed on a table so that Kriss Kringle would have a place to put presents, the Christmas tree grew into a particular kind of technological spectacle. The lights in our trees might seem commonplace or trite, but once upon a time (and a time not long ago, in a place very close to home), they became a symbol of progress and the power of electricity to make light without flames.
We don't often think about it this way, but the modern Christmas tree is a fundamentally technological object. Those strings of lights meant something once upon a time. And they did work in the world, too. Christmas trees became part of how electricity was converted from a dark and mysterious force that occasionally descended from the heavens to kill people into a safe and domesticated product that lit up your living room.
Old world German protestants had decked their trees since the early 17th-century with "roses cut out of many-coloured paper, apples, wafers, gold foil, sweets, &c." By the first few decades of the 1800s, the practices had spread throughout western Europe and, according to Penne Restad's book, Christmas in America, a history, to Pennsylvania, too. By 1821, a Lancaster, Pennsylvania resident named Matthew Zahm could write, "Sally & our Thos. & Wm. Hensel was out for Christmas trees, on the hill at Kendrick's farm." In 1832, a German professor at Harvard put "7 dozen wax tapers, gilded egg cups, paper corncucpiae filled with comfits, lozenges and barley sugar."