How to increment tailSet integers in TreeSetAtomicInteger without addAll ()?

I have the following part of a class:

private TreeSet<AtomicInteger> offsets;

// ...

public void addIndex(int index) {
    SortedSet<AtomicInteger> set = offsets.tailSet(new AtomicInteger(index), false);
    AtomicInteger[] backup = set.toArray(new AtomicInteger[0]);
    set.clear();
    for (AtomicInteger i : backup) {
        i.incrementAndGet();
    }

    offsets.addAll(Arrays.asList(backup));
}

addIndex () basically increments all indexes after index of the set. My question is: can I change the method for this?

public void addIndex(int index) {
    SortedSet<AtomicInteger> set = offsets.tailSet(new AtomicInteger(index));
    for (AtomicInteger i : set) {
        i.incrementAndGet();
    }
}

Because the integers are still in order, then TreeSet would still be right. But this changes the elements outside of the TreeSet, so I'm in doubt.