enum Tree<T> {
   Node(a:Tree<T>, b:Tree<T>);
   Leaf(x:T);
}

...

switch (sometree) {
   case Node(Node(Leaf(x), Leaf(y)), z): // matches against a tree whose left-subtree is a tree with two leaves (whose data is put in x/y), and whose right side can be anything (put in z)
   default:
}

or with consts like:

switch (keycode) {
   case Keyboard.Left:
   case Keyboard.Right:
   ..
}

where Keyboard.Left/Right has to be marked as 'inline static' so that compiler knows it is a constant value that can never change and is interpreted the exact same as:

switch (keycode) {
  case 72:
  case 48:
  ...
}

for whatever value the keycode consts have.