take the example from here
http://www.jeasyui.com/tutorial/tree/treegrid1.php (Create a Basic TreeGrid, easyui-treegrid1-demo.zip)
Change one line in the treegrid1_demo.html
<thead frozen="true">
and expand the MySQL Node. After you expand the MySQL Node there is nor slider on the TreeGrid.
Without the change in the html file you have the slider after expand MySQL.