Better to use any non-toxic Australian species - eucalypt, wattle etc. You DON'T need to bleach or sterilise them at all - this is a nonsense notion promoted by people who don't realise that snakes live in the bush completely surrounded by non-sterilised stuff. They won't get mites, germs or viruses from branches, and even the chance of picking up a tick is probably millions to one!
You may want to, as ZOOJAS suggests, pour boiling water over them, especially if the branch is an old, dead one, simply because they may house ants, which can be a nuisance. Having said that, I have a monitor enclosure which has a large colony of large nocturnal ants living in a log, and has for about 2 years, without there being the slightest conflict between the reptile occupants and the insects. The lizards are out & about during the day, and the ants come out after dark - neither worries the other, and the ants keep the enclosure pretty clean.