Select 2 select all multiselect

How to select all and unselect all options in select I am facing issue that select all option is working fine but when unselect option it could not be unselect Here is my code

     $("#selectAllExtensions").click(function() {
            if ($("#selectAllExtensions").is(':checked')) {
                $("#extensionsId > option").prop("selected", "selected");
                $("#extensionsId").trigger("change");
            } else {
                $("#extensionsId > option").removeAttr("selected");
                $("#extensionsId").trigger("change");
            }
        });