trigger AutoNumberProposal on Quote (after insert) {
   if(trigger.isInsert){
     AutoUpdateProposalName.after_insert(trigger.new);
   }
 }
 //////////////////////////////////////////////
 public class AutoUpdateProposalName {

   public static void after_insert(List<Quote> qtelst){

    List<Quote> lstAccUpdate = new List<Quote>();
    for(Quote objAccount: qtelst)
    {
        objAccount.Name = objAccount.Quote_Auto__c ;
        lstAccUpdate.add(objAccount);
    }
    system.debug('---14---'+lstAccUpdate);
    update lstAccUpdate;
  }

 }