If you are concerned about a tree on a neighbouring property, the best way to sort the issue out is to discuss it with your neighbour. Your neighbour may not be aware that there is an issue.
You are entitled to prune any overhanging branches or the roots of a tree that cross your property from your neighbour's property under the "common law right to abatement."
Pruning should only be done to the minimum extent necessary (up to your property boundary) and in accordance with the Australian Standard for Pruning of Amenity Trees. Pruning must not result in a detrimental impact to the future health or stability of the tree, or compromise the form of the tree.
Any roots, fruit, branches etc. that you remove from your neighbour's tree remain their legal property and the disposal of them should be negotiated with them.
Please Note: You may not enter a neighbouring property to undertake any tree works without the property owner's consent. It is advisable to obtain all consents in writing.