code: void printDotNodesAtLevel(PrintStream os, int levelToPrint, boolean detail, PrintMojo.PrintTreeOptions treeOptions) {
      if (getDepth() == levelToPrint) {
        printDotNode(os, detail, treeOptions);
        return;
      }
  
      assert (getDepth() < levelToPrint);
  
      if (leftChild != null) {
        leftChild.printDotNodesAtLevel(os, levelToPrint, detail, treeOptions);
      }
      if (rightChild != null) {
        rightChild.printDotNodesAtLevel(os, levelToPrint, detail, treeOptions);
      }
    }
docs: Recursively print nodes at a particular depth level in the tree.  Useful to group them so they render properly.
  @param os output stream
  @param levelToPrint level number
  @param detail include additional node detail information