Tree Panel Grouped header is not Working

Hi i am using sandbox (4.0) version to render tree panel

I want to group the column header of tree Panel

But it is not working

here is my code

var treegrid=Ext4.create('Ext4.tree.Panel', {

title: repName,

renderTo:treerender,

//border:false,

rootVisible:false,

columnLines: true,

anchor:'100%',

layout: 'fit',

width:resolutionWidth,

height: 500,

plugins:[new Ext.ux.grid.ColumnHeaderGroup({

rows: leveljson

})],

columns: columnModel,

storetore,

frame:false,

footer:false,

// layout:'fit',

viewConfig: {

forceFit: forcefitFlag,

scrollOffsetcrollOffsetFlag

},

tbar: Ext4.create('Ext4.toolbar.Toolbar', {

hideBorders:true,

id:'tbarmain'+resA["title"],

bodyStyle:'padding:3px',

frame:false,

items:[{

xtype:'tbtext',

text: '<span style="color:black;font-size:11px;font-family:tahoma;font-weight:bold;" ext:qtip="'+reportdescription+'">'+resA["title"]+'</span>'//the description of the report appears when hovering the reportname

}

]})

});

It is coming like this

682BE4EEC76423.jpg

I want like this

EEADE173FB20F9.jpg