@Override
    public String toRankingExpression() {
        StringBuilder expression = new StringBuilder();
        expression.append("if (").append(feature).append(rankingExpressionCondition());
        expression.append(", ").append(left.toRankingExpression());
        expression.append(", ").append(right.toRankingExpression());

        Optional<Float> trueProbability = trueProbability();
        if (trueProbability.isPresent())
            expression.append(", ").append(trueProbability.get());

        expression.append(")");
        return expression.toString();
    }
A node in a GBDT tree which references a feature value

@author bratseth
searchlib/src/main/java/com/yahoo/searchlib/gbdt/FeatureNode.java