Bpmn-js adding custom task

I am using bpmn-js and bpmn-js properties panel.I need to add a custom task in the task element.for e.g after dragging the task element in the space when we click on the wrench icon,several tasks are shown like Send Task,Receive Task,Script Task etc.I want to my custom task to be shown in that list.
Can anyone please guide how to proceed with this?

Please ask bpmn-js questions here: https://forum.bpmn.io/