val tt = Node(1,Node(2,Node(4,Empty,Empty),Empty),Node(3,Node(5,Empty,Node(6,Empty,Empty)),Empty));;


  sealed trait BT[+A]
  case object Empty extends BT[Nothing]
  case class Node[+A](elem:A, left:BT[A], right:BT[A]) extends BT[A]

  def breadthBT[A](tree: BT[A]) = {
    def helper[A](nodeQueue: List[BT[A]]): List[A] = nodeQueue match {
      case Nil => Nil
      case Empty :: tail => helper(tail)
      case Node(value, leftSubtree, rightSubtree) :: tail => value :: helper(tail ++ List(leftSubtree, rightSubtree))
    }
    helper (List(tree))
  }