docs: def _query(self, x, result):
          '''
          Same as self.query, but uses a provided list to accumulate results into.
          '''
          if self.single_interval is None: # Empty
              return
          elif self.single_interval != 0:  # Single interval, just check whether x is in it
              if self.single_interval[0] <= x < self.single_interval[1]:
                  result.append(self.single_interval)
          elif x < self.center:            # Normal tree, query point to the left of center
              if self.left_subtree is not None:
                  self.left_subtree._query(x, result)
              for int in self.mid_sorted_by_start:
                  if int[0] <= x:
                      result.append(int)
                  else:
                      break
          else:  # Normal tree, query point to the right of center
              for int in self.mid_sorted_by_end:
                  if int[1] > x:
                      result.append(int)
                  else:
                      break
              if self.right_subtree is not None:
                  self.right_subtree._query(x, result)