monthAndNumberGroupedAndSorted.fs

let data = [
    ("January", 1);
    ("June", 10);
    ("March", 12);
    ("February", 20);
    ("January", 15);
    ("July", 15)
]

let grouped = 
    data 
    |> List.groupBy fst
    |> List.map (fun (key, group) -> key, group |> List.sumBy snd)
    |> List.map (fun (month, total) -> DateTime.ParseExact(month, "MMMM", CultureInfo.InvariantCulture), total)
    |> List.sortBy (fun (month, _) -> month.Month)
    |> List.map (fun (month, total) -> month.ToString("MMMM"), total)
    |> Dump