appendTo in jquery replace old div insted of add new one under it

I have problem with this code. I am trying to append new div (newGallery) with pictures to div (gallery) but it is still replacing old one.

Can you please advice me how to solve it? I think it has some trouble that it is inside ajax funcion. I am using jquery v3.5.1.

menu.on('click', 'a', function(event) {

    event.preventDefault();

    var a = $(this),
        li = a.parent(),
        href = a.attr('href'),
        loadingImg = $('<img>', {src: 'img/5.svg', class: 'loading-img'}),
        id = '#' + href.slice(0, -5),
        isLoaded = gallery.find(id),
        currentGallery = gallery.find('.gallery-set'),
        galleries = $('.gallery-set');

    if (li.hasClass('selected')) return;

    li.addClass('selected')
      .siblings().removeClass('selected');
    //zobrazenie loading ikony pokial sa obsah nenacita
    gallery.html(loadingImg).show();
    gallery.find('div').fadeOut();

    if ( galleries.attr("id") == id ) {
        currentGallery.hide();
        gallery.find(id).fadeIn();

    } else {
        loadNewGallery(href);
    };

    function loadNewGallery (href) {
        var gallery = $('.gallery');

        $.ajax({
            url: href,
            data: 'GET',
            dataType: 'html',
        // ak sa data nacitaju vykona sa funkcia v done
        }).done( function( data ) {
            var newGallery = $(data).find('.gallery-set');

                //nacitany kus stranky cez ajax sa vlozi do gallery natrvalo
                newGallery.appendTo(gallery);

        // ak sa data nenacitaju vykona sa funkcia vo fail
        }).fail( function() {
            // sprava o zlyhani prenosu
            var msg = $('<div>',{class: 'msg-fail'}),
                msgText = 'Je nám ľúto, danú stránku sa nepodarilo zobraziť',
                msgFail = msg.html(msgText);

            gallery.html(msgFail);
        // aj ked sa data nacitaju alebo nenacitaju vykona sa funkcia v always
        }).always(function() {
            // skrytie loading ikonky
            loadingImg.hide();
        });
    };
});