type GenTree<'data> =
      |Leaf of 'data
      |SubTree of  GenTree<'data> * 'data * GenTree<'data>

    type Calc =
        |Operator of (float->float->float)
        |Operand of float

    let IsOperator (str:string) =
        match str with
        | "+" | "-" | "x" | "/" -> true
        |_ -> false

    let parseToFloat (str:string list) =
        System.Single.Parse <|  System.String.Concat((List.toSeq str))

    let SwapValue (str:string) =
        match str with
        |"+" -> (+)
        |"-" -> (-)
        |"x" -> (*)
        |"/" -> (/)
        |_ -> failwith "Not valid operator"

    let rec ConvertValueTree (list:string list) =
        match list with
        |x::x2::x3::xs when (not (IsOperator x2)) && (not (IsOperator x)) -> x::x2::(ConvertValueTree xs)
        |_ -> failwith "Please insert more information"