copy elements from one listbox to another

copy elements from one listbox to another

I have 2 <select> with many elements. I need when i click in a link that the selected elements duplicate to another <select>.
I can only move or append with this

    $('#addAllDipe').click(function() {
        $('#selectDipendenti option').each(function(i) {
            $('#selectDipendenti option').remove().appendTo('#selectDipendenti2');
        });

I try ro remove the remove() method but nothing change.
Thanks for help