My Trigger is as follows:- 

trigger opportunityAcountTeam on Opportunity (after insert, after update) {
    LIST<Opportunity> listOpp = new LIST<Opportunity>();
    SET<ID> oppIds = new SET<ID>();
    LIST<AccountTeamMember> listAccTeamMember = new LIST<AccountTeamMember>();
    //LIST<AccountShare> listShare = new LIST<AccountShare>();
    if(Trigger.IsAfter && Trigger.IsInsert) {
        for(Opportunity newOpp : Trigger.new) {
            if(newOpp.Probability == 20) { 
                    if(String.isEmpty(newOpp.AccountId)) {
                    newOpp.addError('Account name cannot be blank');
                    return;    
                    }
                listOpp.add(newOpp);
                oppIds.add(newOpp.AccountId);               
                    AccountTeamMember newAccMember = new AccountTeamMember();
                    newAccMember.AccountAccessLevel = 'Edit';
                    newAccMember.OpportunityAccessLevel = 'Read';
                    newAccMember.TeamMemberRole = 'Account Manager';
                    newAccMember.AccountId = newOpp.AccountId;                 
                    newAccMember.UserId = newOpp.OwnerId;
                    newAccMember.Account = newOpp.Account;
                    //AccountShare newAccShare = new AccountShare();
                    //newAccShare.AccountAccessLevel='Read';
                     //newAccShare.OpportunityAccessLevel = 'Read Only';
                     //newAccShare.CaseAccessLevel='Read Only';
                    //newAccShare.AccountId = newOpp.AccountId;
                    //newAccShare.UserOrGroupId = newOpp.OwnerId;                    
                    listAccTeamMember.add(newAccMember);
                    system.debug('team' + listAccTeamMember);
                    //listShare.add(newAccShare);        
                        if(listAccTeamMember != NULL) {
                        insert listAccTeammember;                        
                        }
           }
        }       
    }
}

My test class is as follows:-

@isTest
public class oppAccTeamMember {
    static testMethod Void testOppAccTeamMember() {
        LIST<Opportunity> newOpp = new LIST<Opportunity>();
        LIST<AccountTeamMember> newTeamMember = new LIST<AccountTeamMember>();
        LIST<Account> listAcc = new LIST<ACCOUNT>();
        SET<ID> allIds = new SET<ID>();
        Profile pld= [SELECT Id FROM Profile WHERE Name = 'Standard User' LIMIT 1];
        User u= new User();
        u.LastName = 'ttt';
        u.ProfileId = Pld.Id;        
        insert u;                   
        
        Account newAcc = new Account();
        newAcc.Name = 'Starting';
        newAcc.OwnerId = u.Id;        
        listAcc.add(newAcc);        
        insert listAcc;        
                
        Opportunity createOpp = new Opportunity();       
        createOpp.Name = 'First';
        createOpp.CloseDate = Date.today();
        createOpp.StageName = 'Prospecting';
        createOpp.AccountId = newAcc.Id;
        allIds.add(createOpp.AccountId);
        if(String.isEmpty(createOpp.AccountId)) {
        createOpp.addError('Account name cannot be blank');
        return; 
        }       
       newOpp.add(createOpp);       
       insert newOpp;       
        
        AccountTeamMember createTeam = new AccountTeamMember();
        createTeam.accountId = createOpp.AccountId;
        createTeam.AccountAccessLevel = 'Read';
        createTeam.UserId = createOpp.OwnerId;
        newTeamMember.add(createTeam);        
        insert newTeamMember;       
    }
}

My test class is failing and it is giving me System.DMLException Insert failed

Please provide assistance as I am stuck with for many days and I do not just want to forget about it because by doing that I am not going to learn for the next time.

Thanks
Vijay