private void addTo(List<Double> forest, GBDTNode tree) {
        forest.add((double)tree.values().length);
        addAll(tree.values(), forest);
    }
Optimize the given node, if it is the root of a gdbt forest. Otherwise do nothing and return false
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/gbdtoptimization/GBDTForestOptimizer.java