code: private static PBXObjectRef createPBXGroup(final String name, final String sourceTree, final List children) {
      final Map map = new HashMap();
      map.put("isa", "PBXGroup");
      map.put("name", name);
      map.put("sourceTree", sourceTree);
      map.put("children", children);
      return new PBXObjectRef(map);
    }
docs: Create PBXGroup.
  
  @param name
  group name.
  @param sourceTree
  source tree.
  @param children
  list of PBXFileReferences.
  @return group.