I used an egg carton box to secure the branches in my container. Another idea would be to use a clay type product to stick them in with…. or foam. 🙂

These
are examples of branches I use… if you get them just when they are
budding you will have branches that look really life like (as in still
alive) and they will last you for a long time. Just don’t cut them too
late or the budding leaves will dry & fall off.