code: def find_dependencies(self, dataset_keys, **dfilter):
          
          unknown_datasets = set()
          for key in dataset_keys.copy():
              n, unknowns = self._find_dependencies(key, **dfilter)
  
              dataset_keys.discard(key)  # remove old non-DatasetID
              if n is not None:
                  dataset_keys.add(n.name)  # add equivalent DatasetID
              if unknowns:
                  unknown_datasets.update(unknowns)
                  continue
  
              self.add_child(self, n)
  
          return unknown_datasets
docs: Create the dependency tree.
  
          Args:
              dataset_keys (iterable): Strings or DatasetIDs to find dependencies for
              **dfilter (dict): Additional filter parameters. See
                                `satpy.readers.get_key` for more details.
  
          Returns:
              (Node, set): Root node of the dependency tree and a set of unknown datasets