before Tree
 before -> Tree, l, Label
  at a Label ----before Label
   after Label
  after -> Tree, l, Label
 before -> Tree, left, Tree
  before Tree
   before -> Tree, l, Label
    at a Label ----before Label
     after Label
    after -> Tree, l, Label
   before -> Tree, left, Tree
    before Tree
     before -> Tree, l, Label
      at a Label ----before Label
       after Label
      after -> Tree, l, Label
     before -> Tree, right, Tree
      before Tree
       before -> Tree, l, Label
        at a Label ----before Label
         after Label
        after -> Tree, l, Label
       after Tree
      after -> Tree, right, Tree
     after Tree
    after -> Tree, left, Tree
   before -> Tree, right, Tree
    before Tree
     before -> Tree, l, Label
      at a Label ----before Label
       after Label
      after -> Tree, l, Label
     after Tree
    after -> Tree, right, Tree
   after Tree
  after -> Tree, left, Tree
 after Tree

: Tree  (
	<l> at a Label ----: Label  ( )
	<left> : Tree  (
		<l> at a Label ----: Label  ( )
		<left> : Tree  (
			<l> at a Label ----: Label  ( )
			<right> : Tree  (
				<l> at a Label ----: Label  ( ) ) )
		<right> : Tree  (
			<l> at a Label ----: Label  ( ) ) ) )
done: result = 13,13
 show left trees 
: Tree  (
	<left> : Tree  (
		<left> : Tree  ( ) ) )
 show all trees 
: Tree  (
	<left> : Tree  (
		<left> : Tree  (
			<right> : Tree  ( ) )
		<right> : Tree  ( ) ) )