code: def insert(self, value):
          
          i = 0
          n = len(self._tree)
          while i < n:
              cur = self._tree[i]
              self._counts[i] += 1
              if value < cur:
                  i = 2 * i + 1
              elif value > cur:
                  i = 2 * i + 2
              else:
                  return
          raise ValueError("Value %s not contained in tree." "Also, the counts are now messed up." % value)
docs: Insert an occurrence of `value` into the btree.