Implicit resolution

package foo

object Foo extends App {
  case class Tree(label: String, children: List[Tree])
  
  trait Show[T] {
    def show(t: T): String
  }
  
  implicit def listShow[T : Show]() = new Show[List[T]]{
    def show(ts: List[T]) = "(" + ts.map(t => implicitly[Show[T]].show(t)).mkString(" ") + ")"
  }
  
  implicit val treeShow = new Show[Tree] {
    def show(t: Tree) =
      t.label +
      listShow[Tree].show(t.children) // doesn't compile
      
      // could not find implicit value for evidence parameter of type foo.Foo.Show[foo.Foo.Tree]
      // not enough arguments for method listShow: (implicit evidence$1: foo.Foo.Show[foo.Foo.Tree])foo.Foo.Show[List[foo.Foo.Tree]]. Unspecified value parameter evidence$1.
  }
}