trigger TriggerNew1Problem on Account(after insert)
{
    Set<String> setacc = new Set<String>();
    for(Account a : Trigger.new)
    {
        setacc.add(a.Name);
    }
    
    List<Account> acclist = [Select Id, Name, (Select Id, Name From Opportunities)
    From Account Where Name In : setacc
    ];
    List<Opportunity> opplist = new List<Opportunity>();
    
    Map<String, Account> nmap = new Map<String, Account>();
    for(Account a : acclist)
    {
        nmap.put(a.Name, a);
    }
    
    for(Account acc : Trigger.new)
    {
        if(nmap.get(acc.Name)!=null)
        {
            opplist.add(new Opportunity(AccountId =acc.Id, Name ='Duplicate Opportunity'+acc.Name, StageName = 'prospecting'
            , CloseDate = System.today()));         
        }
        else if(nmap.get(acc.Name)==null)
        {
             opplist.add(new Opportunity(AccountId =acc.Id, Name ='First Opportunity'+acc.Name, StageName = 'prospecting'
            , CloseDate = System.today()));
        }
    }
    if(opplist.size()>0)
    {
        insert opplist;
    }
}

when i inserted duplicate name in account then print duplicate opportunity name on the bases of account if not a duplicate account name then print first opportunity
But First Opportunity is not printed