How do I sort a List of TreeSets with java8 streams

My list contains sets like [1,3,5][2,6,4] etc, all of the same size. I tried doing this but it doesn't seem to work.

List<TreeSet<T>> block;
    for(TreeSet<T> t : block){
        block.stream().sorted((n,m)->n.compareTo(m)).collect(Collectors.toSet());

    }

The end result I want is [1,2,3][4,5,6].

I could try to add all the elements in an ArrayList and sort that out then make a new List of TreeSet's. But is there is some kind of one liner?

UPDATE:

List<T> list=new ArrayList<T>();
    for(TreeSet<T> t : block){

        for(T t1 : t)
        {
            list.add(t1);   

        }
    }

    list=list.stream().sorted((n,m)->n.compareTo(m)).collect(Collectors.toList());

This works but could this be simplified?