I think you need something like:
$('#menu-btn').click(function(event) {
$('#whole').animate({
left: '100px'
},500,
function(){
$('#data').slideDown();
});
});
Slide down the whole instead if that is what you were thinking.
I updated the fiddle. You had .#whole
instead of #whole
which prevented that style.
EDIT:
See my forked fiddle for a nicer solution: http://jsfiddle.net/6ETK8/6/
Or using css transitions: http://jsfiddle.net/6ETK8/7/