Print elements of binary search tree

bst-node.scala

case class BSTNode(payload: Int, left: Option[BSTNode] = None, right: Option[BSTNode] = None)

object Treeutils {
  def inOrder(root: Option[BSTNode]): List[Int] = root match {
    case None => List()
    case Some(BSTNode(payload, left, right)) => inOrder(left) ::: List(payload) ::: inOrder(right)         
  }
}

scala> val tree = BSTNode(10,Some(BSTNode(8,Some(BSTNode(7,Some(BSTNode(6,None,None)),Some(BSTNode(7,None,None)))),Some(BSTNode(9,None,None)))),Some(BSTNode(11,None,None)))

scala> Treeutils.inOrder(Option(tree))
res0: List[Int] = List(6, 7, 7, 8, 9, 10, 11)