class_docstr: Structure to discover and store `Dataset` dependencies.
  
  Used primarily by the `Scene` object to organize dependency finding.
  Dependencies are stored used a series of `Node` objects which this
  class is a subclass of.
class_docstr_tok: ["Structure","to","discover","and","store","`","Dataset","`","dependencies",".","Used","primarily","by","the","`","Scene","`","object","to","organize","dependency","finding",".","Dependencies","are","stored","used","a","series","of","`","Node","`","objects","which","this","class","is","a","subclass","of","."]
docstr: Determine optional prerequisite Nodes for a composite.
  
  Args:
      parent (Node): Compositor node to add these prerequisites under
      prereqs (sequence): Strings (names), floats (wavelengths), or
                          DataQuerys to analyze.
docstr_tok: ["Determine","optional","prerequisite","Nodes","for","a","composite",".","Args",":","parent","(","Node",")",":","Compositor","node","to","add","these","prerequisites","under","prereqs","(","sequence",")",":","Strings","(","names",")",",","floats","(","wavelengths",")",",","or","DataQuerys","to","analyze","."]
code: def _create_optional_subtrees(
      self, parent, prereqs, query=None
  ):  # noqa: D417
      """Determine optional prerequisite Nodes for a composite.
  
      Args:
          parent (Node): Compositor node to add these prerequisites under
          prereqs (sequence): Strings (names), floats (wavelengths), or
                              DataQuerys to analyze.
  
      """
      (
          prereq_nodes,
          unknown_datasets,
      ) = self._create_prerequisite_subtrees(parent, prereqs, query)
  
      for prereq, unknowns in unknown_datasets.items():
          u_str = ", ".join([str(x) for x in unknowns])
          LOG.debug(
              "Skipping optional %s: Unknown dataset %s",
              str(prereq),
              u_str,
          )
  
      return prereq_nodes
  
imports: from __future__ import annotations
  from typing import Container, Iterable, Optional
  import numpy
  from satpy import DataID, DatasetDict
  from satpy.dataset import ModifierTuple, create_filtered_query
  from satpy.dataset.data_dict import TooManyResults, get_key
  from satpy.node import EMPTY_LEAF_NAME, LOG, CompositorNode, MissingDependencies, Node, ReaderNode
label_desc: Use image node_id 22 for calling the DependencyTree obj's underlying member method code with example usage: obj._create_optional_subtrees(parent, prereqs, query) and returns: prereq_nodes