code: def fetchMore(self, parentIndex):  # TODO: Make LazyLoadRepoTreeModel?
          
          parentItem = self.getItem(parentIndex)
          if not parentItem:
              return
  
          if not parentItem.canFetchChildren():
              return
  
          # TODO: implement InsertItems to optimize?
          for childItem in parentItem.fetchChildren():
              self.insertItem(childItem, parentIndex=parentIndex)
  
          # Check that Rti implementation correctly sets canFetchChildren
          assert not parentItem.canFetchChildren(), \
              "not all children fetched: {}".format(parentItem)
docs: Fetches any available data for the items with the parent specified by the parent index.