src/main/java/org/organicdesign/fp/collections/PersistentTreeSet.java
public static <T extends Comparable<T>> PersistentTreeSet<T> of(Iterable<T> items) {
        // empty() uses default comparator
        if (items == null) { return empty(); }
        PersistentTreeSet<T> ret = empty();
        for (T item : items) {
            ret = ret.put(item);
        }
        return ret;
    }
public static <T extends Comparable<T>> PersistentTreeSet<T> of(Iterable<T> items) {
        // empty() uses default comparator
        if (items == null) { return empty(); }
        PersistentTreeSet<T> ret = empty();
        for (T item : items) {
            ret = ret.put(item);
        }
        return ret;
    }
Returns a new PersistentTreeSet of the given comparable items.