Trans-Siberian Orchestra is celebrating the 20th anniversary of its rock opera “The Lost Christmas Eve” this holiday season on a tour that’s now sold 20 million tickets and, in doing so, surpassed more than $20 million in charity donations.

Those numbers — 20 million tickets sold in 20 years — would seem to be impossible for a production that tours for only two months of the year. But TSO has a secret weapon. Make that two not-so-secret weapons.

“The first thing is most people don’t realize we have two different touring groups,” TSO music director and lead guitarist Al Pitrelli said in a late-September interview. “There’s a West Coast and East Coast group. So when you look at that schedule, it’s literally impossible for one band to cover all that.

“We’ve been doing this with two bands ever since the year 2000, but we play to roughly 1 million people a year between the two groups,” he added. “Along with that is the charity, the dollar per ticket.”

TSO, which returns Sunday to Colorado Springs for a pair of shows at The Broadmoor World Arena, is known for its lavish productions that showcase a rock show complete with pyro and lasers together with the performance of music and story written by TSO’s late founder, Paul O’Neill.

For Pitrelli and drummer Jeff Plate, TSO grew up out of a single song — “Christmas Eve/Sarajevo 12/24” — the group recorded for its debut album, “Christmas Eve and Other Stories.”

Plate knew that song was special.

“When we recorded this song, there was no denying when you heard it, it was fantastic,” Plate said. “You hadn’t heard anything like it. Christmas music up to that point had been relatively safe. Even if a rock band was doing a Christmas song, they really sugared it up quite a bit. There wasn’t much of an edge to it. That song certainly had an edge.”

“Christmas Eve and Other Stories” (featuring “Christmas Eve/Sarajevo 12/24”) went platinum. So did 1998’s “The Christmas Attic,” setting the table for TSO’s groundbreaking holiday tours.

Now TSO, with its stories and music, has become a holiday tradition for the thousands who come to the shows each year. It’s also a tradition for Pitrelli and Plate.

“It has become like ‘It’s a Wonderful Life’ or, in my case, ‘A Charlie Brown Christmas’ where I want that comfort of the familiarity of my holiday tradition to remind myself,” Pitrelli said. “But, to be honest, becoming families’ holiday tradition was never on my radar.”