In generally, we use reference set selector for this. A reference selector with checkboxes will appear in the AppStore some day :)
Thanks for the solution. I was able to add "Bootstrap multi select" widget in the form. But while defining properties for the same- able to select data source entity (Multi select source) but unable to select attribute (Display attribute). what can be the cause? when I click on select for display attribute, I am not getting attributes listed in the hierarchy. What can be done to select attribute? can someone guide me on this?