The Gemara says:
אין עושין מצות חבילות חבילות
One does not make mitzvot into bundles.
But I've seen lots of people do just that: They put the four species into a bundle.
ואם תומר, and if you'll say:
The issue is making a Mitzva into a bundle, not putting the Mitzvah into a bundle.
You can't say that since the bundle is made from Lulav leaves. So we quite literally made a Mitzvah into a bundle.
Oh, and there are some who only make a bundle out of the Lulav, without even making a basket.
That should definitely be an issue.