code: def _get_merged_bbox(
      pred1: ObjectPrediction, pred2: ObjectPrediction
  ) -> BoundingBox:
      box1: List[int] = pred1.bbox.to_xyxy()
      box2: List[int] = pred2.bbox.to_xyxy()
      bbox = BoundingBox(box=calculate_box_union(box1, box2))
      return bbox
  
imports: import copy
  from typing import List
  import numpy
  from sahi.annotation import BoundingBox, Category, Mask
  from sahi.postprocess.utils import calculate_area, calculate_box_union, calculate_intersection_area
  from sahi.prediction import ObjectPrediction
label_desc: Use image node_id 4 for calling the UnionMergePostprocess obj's underlying member method code with example usage: obj._get_merged_bbox(pred1, pred2) and returns: bbox