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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def find_dependencies(self, dataset_keys, **dfilter):
 """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 """

        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