Thanks for your response Gary, you helped me figure it out:

@using  Our.Umbraco.Vorto.Extensions
@inherits Umbraco.Web.Macros.PartialViewMacroPage

@{ var selection = CurrentPage.Site(); }
@Traverse(selection)
@helper Traverse(dynamic node){
    var maxLevelForSitemap = 4;
    var selection = node.Children.Where("menuweergave == true").Where("Level <= " + maxLevelForSitemap);
    var selectionLevel = node.Level;
    if (selection.Any())
    {
        <ul>
            @if(selectionLevel == 1){
                <li class="menu_li_2"><a href="/">Home</a></li>
            }
            @foreach (var item in selection.Where("menuweergave == true")){
            IPublishedContent sitem= (IPublishedContent)item;
            <li class="menu_li_@item.Level"><a href="@item.Url">@sitem.GetVortoValue("paginatitel")</a>
                 @Traverse(item)
            </li>
            }
        </ul>
    }
}

I added another variable called selectionLevel to get the node.Levelvar selectionLevel = node.Level;. Then i addd this if statement:

        @if(selectionLevel == 1){
            <li class="menu_li_2"><a href="/">Home</a></li>
        }

I couldnt use your suggestion because it would add another <li>home</li> to each var item. But it helped me realise what i was doing wrong, thanks!