The staff at Wrest Park believe their Giant Redwood, planted in 1856, is - and they are decorating it for the first time in a century this week.
The 100ft tree, a Sequoiadendron giganteum, is native to California and is the largest, and longest living species in the world.
It was planted in the grounds in 1856 and was used each Christmas until it grew too big to be bought indoors.
It stood forgotten in the park for decades until English Heritage gardeners found a reference to its use as a Christmas tree during the Victorian era in an edition of Gardener’s Chronicle, from June, 1900.
The article said it was planted by the appropriately-named Seward Snow, in 1856, and must have been one of the first introduced to the country.
It added: “Mr Ford, the late gardener at Wrest Park ... has carried the plant many times from the conservatory to the mansion, and vice versa.”
With the help of a cherry-picker, staff have now placed a star on the tree and are inviting visitors to help decorate the lower branches with traditional ribbons during December.
If you know of an older living Christmas tree, email Christmas@english-heritage.org.uk the details and a photograph.