docs: def reroot(self, rppr=None, pretend=False):
          """Reroot the phylogenetic tree.
  
          This operation calls ``rppr reroot`` to generate the rerooted
          tree, so you must have ``pplacer`` and its auxiliary tools
          ``rppr`` and ``guppy`` installed for it to work.  You can
          specify the path to ``rppr`` by giving it as the *rppr*
          argument.
  
          If *pretend* is ``True``, the convexification is run, but the
          refpkg is not actually updated.
          """
          with scratch_file(prefix='tree', suffix='.tre') as name:
              # Use a specific path to rppr, otherwise rely on $PATH
              subprocess.check_call([rppr or 'rppr', 'reroot',
                                     '-c', self.path, '-o', name])
              if not(pretend):
                  self.update_file('tree', name)
          self._log('Rerooting refpkg')