docs: public CfgParseTree multiplyProbability(double amount) {
      if (isTerminal()) {
        return new CfgParseTree(root, ruleType, terminal, getProbability() * amount, spanStart, spanEnd);
      } else {
        return new CfgParseTree(root, ruleType, left, right, getProbability() * amount);
      }
    }