with the following change to TreeBinder :

PHP Code:
public void setCheckedProperty(String checkProp) {
    
this.checkPropcheckProp;
}

protected 
TreeItem createItem(ModelData model){
... 
     if (
model.get(checkProp) !=null ) {
         
item.setChecked((Boolean)model.get(checkProp));
     } 
...