Get the c++ PhyloTree object corresponding to this tree.
        :return: PhyloTree instance

def phylotree(self):
        """
        Get the c++ PhyloTree object corresponding to this tree.
        :return: PhyloTree instance
        """
        if not self._phylotree or self._dirty:
            try:
                if ISPY3:
                    self._phylotree = PhyloTree(self.newick.encode(), self.rooted)
                else:
                    self._phylotree = PhyloTree(self.newick, self.rooted)
            except ValueError:
                logger.error('Couldn\'t convert to C++ PhyloTree -- are there bootstrap values?')
            self._dirty = False
        return self._phylotree