if you need to change some information you can use this one
trigger CloneWorkorder on Work_Order__c (after insert) {
List<Work_order__c> CaLNewList = new List()<Work_order__c>;
for (Work_order__c WorkOrder : Trigger.new) {
CaLNewList.add(new work_order__c(case__c = workOrder.case__c));
}
insert CaLNewList;
}
OR if you need exactly same copy
trigger CloneWorkorder on Work_Order__c (after insert) {
List<Work_order__c> CaLNewList = trigger.new.deepClone();
insert CaLNewList;
}