Olive wood should be safe, just remember to choose a healthy tree that hasn't been treated with pesticides. If you don't know whether or not the tree has been treated with pesticides, than it is a good idea to be on the safe side, and
not use it. If the tree is safe, you will need to clean the branches thoroughly to remove any mold or bugs that could be toxic or fatal to your bird. To clean the branches soak them in vinegar for several hours to kill the bugs. Then put the branches in the oven at 200 degrees for 1-2 hours. Finally, place the branches in a dry, safe place and leave them out in the sun for several days. This is the link to where I got the directions:
How To Use Natural Tree Branches In Your Bird's Cage I know it seems like a lot of work but it's much better to be safe than sorry.