3 answers
hi srikanth, you made some mistake replace your second contact object with following code.
Contact con1 = new Contact();
con1.LastName = 'Test2';
con1.AccountId = Acc.Id;
con1.Sum__c = 200;
conList.add(con1);
insert conList;
you forget add con1 in lastName.
let me know if it helps you and marking it as best.Thank you