code: def get_tree(self, tgt_env):
          '''
          Return a tree object for the specified environment
          '''
          if not self.env_is_exposed(tgt_env):
              return None
  
          tgt_ref = self.ref(tgt_env)
          if tgt_ref is None:
              return None
  
          for ref_type in self.ref_types:
              try:
                  func_name = 'get_tree_from_{0}'.format(ref_type)
                  func = getattr(self, func_name)
              except AttributeError:
                  log.error(
                      '%s class is missing function \'%s\'',
                      self.__class__.__name__, func_name
                  )
              else:
                  candidate = func(tgt_ref)
                  if candidate is not None:
                      return candidate
  
          # No matches found
          return Nonf get_tree(self, tgt_env):
          '''
          Return a tree object for the specified environment
          '''
          if not self.env_is_exposed(tgt_env):
              return None
  
          tgt_ref = self.ref(tgt_env)
          if tgt_ref is None:
              return None
  
          for ref_type in self.ref_types:
              try:
                  func_name = 'get_tree_from_{0}'.format(ref_type)
                  func = getattr(self, func_name)
              except AttributeError:
                  log.error(
                      '%s class is missing function \'%s\'',
                      self.__class__.__name__, func_name
                  )
              else:
                  candidate = func(tgt_ref)
                  if candidate is not None:
                      return candidate
  
          # No matches found
          return None
docs: Return a tree object for the specified environment