Transform a collection

Have a collection of objects. Schematically:

[
    { A = 1, B = 1 }
    { A = 1, B = 2 }
    { A = 2, B = 3 }
    { A = 2, B = 4 }
    { A = 1, B = 5 }
    { A = 3, B = 6 }
]

Need:

[
    { A = 1, Bs = [ 1, 2 ] }
    { A = 2, Bs = [ 3, 4 ] }
    { A = 1, Bs = [ 5 ] }
    { A = 3, Bs = [ 6 ] }
]

Is it possible to LINQ such?

Note: Ordering is important. So Bs = [5] can't be merged with Bs = [1, 2]