Try this:
<script>
$.extend($.fn.treegrid.methods, {
myRefresh: function(jq){
return jq.each(function(){
var t = $(this);
var opts = t.treegrid('options');
var n = t.treegrid('getSelected');
var d = t.treegrid('getData');
t.treegrid('loadData', d);
if (n){
t.treegrid('select', n[opts.idField]);
}
})
}
});
</script>
Now you can call 'myRefresh' method.
$('#tg').treegrid('myRefresh');