code: func (w *TreeWalker) Tree() *Tree {
  	current := len(w.stack) - 1
  	if w.stack[current].pos == 0 {
  		current--
  	}
  
  	if current < 0 {
  		return nil
  	}
  
  	return w.stack[current].t
  }
docs: // Tree returns the tree that the tree walker most recently operated on.