Avoid any plant/ tree that has white sap or is known to be poisonous.
Deciduous tree (ones that drop leaves in autumn) are fine and so are Eucalypts.
Most trees are fine, just let the wood dry for a few months and then soak it in a bucket of water. Once the wood has become water logged and sinks, add a couple of shrimp or cheap fish and see if they live. If they die then the wood is not suitable.