Can any one help with this - where am i going wrong?

trigger AutoCreateSA on Opportunity (after insert , before update,after update)
{
List<Service_Agreement__c> listSA = new List<Service_Agreement__c>();
List<Commission_Tracking__c> listCOM = new List<Commission_Tracking__c>();
        
        for(Opportunity o : trigger.new)
        {
            if(Trigger.isUpdate)
            {
                if(o.StageName == 'Closed Won' && o.SA_Generated__c == FALSE)
                {
                  listSA.add(new Service_Agreement__c(
                  name = o.Name + ' - ' + o.Service_Type2__c,
                  Related_Account__c = o.accountid,
                  Related_Opportunity__c = o.id,
                  BD_Owner__c=o.OwnerId,
                  DEBUG_BDApprovalREQ__c=o.Sales_Script_Approval_Req__c,
                  Primary_Contact__c = o.Primary_Opportunity_Contact__c));
                  listCOM.add(new Commission_Tracking__c(
                  Opportunity__c = o.Id));
                  
                                 }
            }
            if(Trigger.isInsert)
            {
                if(o.StageName == 'Closed Won' && o.SA_Generated__c == FALSE)
                {
                 listSA.add(new Service_Agreement__c(
                  name = o.Name + ' - ' + o.Service_Type2__c,
                  Related_Account__c = o.accountid,
                  Related_Opportunity__c = o.id,
                  BD_Owner__c=o.OwnerId,
                  DEBUG_BDApprovalREQ__c=o.Sales_Script_Approval_Req__c,
                  Primary_Contact__c = o.Primary_Opportunity_Contact__c));
                  listCOM.add(new Commission_Tracking__c(
                  Opportunity__c = o.Id));
                  
                }
            }
        
        if(listSA.size() > 0)
        {
            o.SA_Generated__c = TRUE;
        }
            
        if(listSA.size() > 0)
        {
            insert listSA;
        }
        if(listCOM.size() > 0)
        {
            insert listCOM;
        }
        }
}