extjs 4 show mask while check/uncheck nodes

im trying to check/uncheck specific node and its child nodes as below it is working. Except loading mask. i don't know what is the problem. why not show the mask ?

Code:

onTreepanelCheckChange: function(node, checked, eOpts) {    
tree.setLoading( 'Wait...' );    
node.cascadeBy( function( n ) {        
n.set( 'checked', checked );        
if( n.data.p_id !== 0 ) n.expand();    
} );    
tree.setLoading( false );
}

I've tried to use tree.suspendLayouts(); before cacadeBy function but result is same



extjs 4 show mask while check/uncheck nodes