@Override
    public Predicate process(Predicate predicate, PredicateOptions options) {
        return simplifyTree(predicate);
    }
Simplifies Disjunction nodes where all children are of type FeatureSet. All FeatureSet that share the same key
are merged into a single FeatureSet. The Disjunction is removed if all children merges into a single feature set.

@author bjorncs
predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/OrSimplifier.java