List<Work_Order__c> woList =  [Select id,
                                               (Select Id,
                                                     IsPending,
                                                     ProcessInstanceId,
                                                     TargetObjectId,
                                                     StepStatus,
                                                     OriginalActorId,
                                                     ActorId,
                                                     RemindersSent,
                                                     Comments,
                                                     IsDeleted,
                                                     CreatedDate,
                                                  CreatedById,

                                                     SystemModstamp
                                               FROM ProcessSteps
                                          ORDER BY CreatedDate DESC)
                                                From Work_Order__c
                                            WHERE Id IN : Trigger.new];

         if(woList.size() > 0){
           for(Work_Order__c wo : woList){
            for(Work_Order__c wo1 : Trigger.new) {

                     if(wo.id == wo1.id && wo1.copy_comment__c ) {
                       if (wo.ProcessSteps.size() > 0) {

                     wo1.Approver_Comment__c = wo.ProcessSteps[0].Comments;
                     wo1.copy_comment__c = false;
                     }

                    }

                }
           }
         }

}

if(woList.size() > 0){
                       if (wo.ProcessSteps.size() > 0) {

                     wo.Approver_Comment__c = wo.ProcessSteps[0].Comments;
                     wo.copy_comment__c = false;
                       }}}}