President Kennedy & Jacqueline Kennedy displayed this official tree as part of the Nutcracker Theme of 1961 inaugurating the idea of a theme. Barbara Bush repeated the Nutcracker Suite theme in 1990. Hillary Clinton took another swing at the popular Nutcracker theme in 1996.
This is the 2007 delivery of a Fraser Fir with Laura Bush as she kicked off the Holiday in the National Parks theme that required an ornament to commemorate each of the 391 National Park Service sites.
Update: Here is another link explaining a bit more about the White House Holiday planning process that picked up steam in July.