Recursive Max in Scala

def recursiveMax(xs: List[Int]): Int = 
    def compareMax(x: Int, y: Int): Int = 
        if (x > y) x
        else y
    if (xs.isEmpty) 0
    else compareMax(xs.head, recursiveMax(xs.tail))

recursiveMax(List(2, 6, 1, 6, 8, 10, 11, 0, 11, 20, 20))

// res0: Int = 20