LAWRENCE, Kan. – Todd Brabender remembers the December nearly 20 years ago when he and some University of Kansas friends gathered around a Christmas tree that was hanging upside-down from a water pipe in his apartment.

It seemed like such a crazy idea then. But not anymore.

The centerpiece of holiday decorating is more often being inverted – hung from the ceiling or mounted bottom-up on the wall – by those looking to save space, more prominently display pricey ornaments or simply distinguish their Christmas tree from so many millions of others.

Upscale retailer Hammacher Schlemmer sold out of its $599.95 pre-lit inverted tree, a 7-foot evergreen that rises from a weighted base, before the end of October. Online tree seller ChristmasTreeForMe.com has sold out of two of its four upside-down models. Tree importer Roman Inc. sold out, too.

“This has turned into a worldwide deal,” said Bill Quinn, owner of Dallas-based ChristmasTreeForMe.

Odd as it may sound, the trend may have originated long ago. Legend has it that a seventh-century English monk went to Germany and used the triangular shape of the fir tree to explain the Christian belief in the Holy Trinity. Converts came to revere the fir, and by the 12th century, the story goes, it was being hung from ceilings at Christmas.

But few believe history is moving the trees out of warehouses and into living rooms.

“My suspicion is that the vast majority are buying them because they seem to be nontraditional,” said Edward O’Donnell, an expert on Christmas traditions and history professor at College of the Holy Cross in Worcester, Mass. “It’s funny and it’s off the wall. Or off the ceiling.”

Consumers began buying overturned trees after seeing them on display in stores, said Dan Loughman, a vice president of product development at Roman Inc., which stocks about 200 kinds of trees.

Retailers use the trees because they take up less floor space, put more ornaments at eye level, and provide additional room to stack merchandise at the bottom – or, actually, the top.

“They want to replicate what they see in the store,” Loughman said. “They go in a store and see a tree with red and white ornaments, they want that. Now that they’re seeing the red and white ornaments on an upside-down tree, they want to replicate that.”

Retailers that carry the upside-down trees – including Target – say they expect sales to grow next season, in part because of their scarcity and publicity this year.