Simple way to get all possible merges of two lists in Haskell

AllMerges.hs

allMerges :: [a] -> [a] -> [[a]]
allMerges [] ys = [ys]
allMerges xs [] = [xs]
allMerges left@(x:xs) right@(y:ys) = 
    map (x:) (allMerges xs right) ++ map (y:) (allMerges left ys)

-- > f [1,2,3] [11,12,13]

-- [   [1,2,3,11,12,13],
--     [1,2,11,3,12,13],
--     [1,2,11,12,3,13],
--     [1,2,11,12,13,3],
--     [1,11,2,3,12,13],
--     [1,11,2,12,3,13],
--     [1,11,2,12,13,3],
--     [1,11,12,2,3,13],
--     [1,11,12,2,13,3],
--     [1,11,12,13,2,3],
--     [11,1,2,3,12,13],
--     [11,1,2,12,3,13],
--     [11,1,2,12,13,3],
--     [11,1,12,2,3,13],
--     [11,1,12,2,13,3],
--     [11,1,12,13,2,3],
--     [11,12,1,2,3,13],
--     [11,12,1,2,13,3],
--     [11,12,1,13,2,3],
--     [11,12,13,1,2,3]
-- ]