If you stuffed the tube into the tire and inflated it, it might have had a small fold in it that got trapped and split.
When you inflate the tube the first time, you should inflate it slowly and only a little bit, massage the tire to release any kinks or folds, then slowly increase pressure until about half way. Then give it another massage and deflate it. Then you can slowly refill it all the way.
If you stuffed the tube into the tire and inflated it, it might have had a small fold in it that got trapped and split.
When you inflate the tube the first time, you should inflate it slowly and only a little bit, massage the tire to release any kinks or folds, then slowly increase pressure until about half way. Then give it another massage and deflate it. Then you can slowly refill it all the way.