Answer: Jacqueline Kennedy
Historically, the Christmas decorations in the White House, including the trees, were simply adorned with the traditions of the time. At that time First Lady Jacqueline Kennedy began in 1961 with the selection of a theme for the official Christmas tree of the White House.
The tree, which was placed in the Blue Room, was adorned with ornamental toys, birds, and birds angels after the iconic Christmas ballet by Pyotr Tchaikovsky The Nutcracker . The next year, the tree had a common theme of "childhood" and showed ornaments made by disabled and older Americans. In this way, the First Lady began not one but two traditions: selecting a theme for the tree and using the tree as a way to connect American citizens, often the needy or marginalized, with the holiday traditions of the White House. 1
If you are curious about others years, or if you just want to take a focused walk through the history of the White House, one tree at a time, here you can see half a century trees.
Courtesy of the White House / John F. Kennedy Presidential Library / Wikimedia.