The Christmas tree on the U.S. Capitol's west lawn was lit Tuesday night.
Fourth-grader Chris Gabrielsen won a statewide contest in Montana to help House Speaker Nancy Pelosi light the tree.
The tree is 78 feet tall and, experts said, 144 years old.
Montana residents made 5,000 ornaments for the tree, which also is decorated with 10,000 energy-saving LED lights.
The tree will be lit every night through Dec. 28.