Obama noted he was to have planted the sapling, the state tree of Illinois, during a scheduled 2010 visit he had to cancel.
"I'm honored," he said. "A white oak from Illinois ... ."
Obama and Ambassador Jeffrey L. Bleich jointly unveiled a plaque showing that the president had dedicated the tree.
The ambassador divulged the oak was doing fine after a rough start.
"It was looking like that Charlie Brown Christmas tree -- a little sad," the ambassador said.
Obama was greeted by the embassy staff and Bleich provided a bit of its link to celebrity history, saying actor Jackie Chan "grew up in the house." Chan's father was a chef for the U.S. Embassy.