Ok I guess you are using pure row selections without checkboxes.
selectionModel: { type: 'row' }
Please try either of the below solutions.
beforeCellClick: function(evt, ui){
var target = evt.originalEvent.target;
if($(target).hasClass("pq-group-icon") ) {
this.Tree()[ui.rowData.pq_close? 'expandNodes': 'collapseNodes']([ui.rowData])
return false;
}
},
or
beforeCellClick: function(evt, ui){
var target = evt.originalEvent.target;
if( $(target).hasClass("pq-group-icon") ) {
this.one('beforeRowSelect', function(){
return false;
});
}
},