Delete Descendant Task
use unlink() method
@api.multi
    def unlink(self):
        parent= self.search([('parent_id''in'self.ids)])
        for child in parent:
            child.unlink()
        return super(ProjectTask, self).unlink()

@api.multi 
 is considered to be used when you need to do something with model itself and don't need to modify/check some exact model's record/records. For example there could be method that returns some meta info about model's structure or some helper methods, etc

Aplikasi Display Jadwal Sholat Odoo 14