The U.S. Treasury Department is considering the sale of a $2.2 billion investment in Citigroup Inc.’s junior debt, aiming to lock in a profit from the lender’s 2008 bailout, people briefed on the matter said. Treasury officials have sought input from financial advisers on how to best dispose of the securities, known as trust preferreds, said the people, who declined to be identified because the talks are private. One question: Whether a sale should take place before or after the government sells the 27 percent equity stake it owns in the New York-based bank.