trigger OpportunityAfterTrigger on Opportunity(after update, after insert){
map<Id, List<Decimal>> accIdOppAmtMap = new map<Id, List<Decimal>>();
List<Account> accListToUpdate = new List<Account>();
    for(Opportunity opp : Trigger.new){
        accIdOppAmtMap.put(opp.accountId, new List<Decimal>());

    }
if(accIdOppAmtMap.size() > 0){

    List<Opportunity> oppList = [Select AccountId, Amount From Opportunity Where AccountId IN : accIdOppAmtMap.keySet() Order By Amount DESC] ; 

 for(Opportunity opp : oppList){
if(accIdOppAmtMap.ContainsKey(opp.AccountId)){
    accIdOppAmtMap.get(opp.AccountId).add(opp.Amount);
}
 }
}
 for(Id accId : accIdOppAmtMap.KeySet()){
    Account acc = new Account(Id = accId);
    if(accIdOppAmtMap.get(accId).size() > 1){
        acc.AnnualRevenue = accIdOppAmtMap.get(accId).get(1);
    } else{
        acc.AnnualRevenue = accIdOppAmtMap.get(accId).get(0);
    }
    accListToUpdate.add(acc);
 }
 update accListToUpdate; 

}