Would someone be able to tell me what sort of tree branches to use in an aviary and do I have to do anything to them before they go into the aviary?

Gum tree branches & fruit tree limbs, make good perches.

wash them in a water vinegar solution and let them dry in the sun, this kills off any harmful bacteria that may make your birds sick

i use gum and fruit trees from my own trees

I use gumtree branches too. My budgies also like hibiscus so we cut large sections of that off our large hibiscus a couple of times a week. They shred and eat the leaves and use the rest like a playgym

I use gum tree branches and bottlebrush branches. They are good for their feet apparently because the width is uneven all over the branch so their feet aren't in the same position all the time.

I use gum tree branches too! Another fun way to make perches is with some natural sisal or cotton rope (untreated), cheap and easy rope perches.