code: public function insideSubtree($node) {
      return (
        $this->getLeft()  >= $node->getLeft()   &&
        $this->getLeft()  <= $node->getRight()  &&
        $this->getRight() >= $node->getLeft()   &&
        $this->getRight() <= $node->getRight()
      );
    }
docs: Checks wether the given node is a descendant of itself. Basically, whether
  its in the subtree defined by the left and right indices.
  
  @param \Baum\Node
  @return boolean