I do not recommend collecting branches that have already fallen off trees.
The risk of them being infested with things is much higher, and they will not last as long for you in your setup.
Instead, break/cut some from live trees.
Clean off all the leaves, and any smaller branches that may not support the weight of your chameleon.
Inspect it for holes, where insects may have burrowed into it.
Check for insects where you broke/cut it off the tree as well.
If you suspect anything is living in it, I would recommend not using it, but you could bake it to kill them if you like.
You can also use a diluted bleach solution to clean them off as well.
Just make sure it dries out well after the cleaning, and is rinsed well.
I dont bake, or use any chemicals to clean my branches/vines.