Dollar Tree’s decade-long effort to fold the Family Dollar chain into its business is ending after agreeing to sell the bargain store chain to a pair of private equity firms for $1 billion.

Dollar Tree, Inc. Also on Wednesday, Dollar Tree reported a net loss of $1.71 billion, or $7.85 per share in the quarter ended Feb. 3, compared with a year-ago profit of $452.2 million, or $2.04 ...