AusBonsai

Any thoughts, please? It's not deciduous and it shoots like crazy when cut back. I acquired it as a very tall, skinny nursery reject and it's exploded since I cut it down to a bare stump at the end of winter.

Luke.

Could be Acacia melanoxylon. The immature and mature leaves look similar to yours.

Almost certainly an Acacia. They all have that ferny juvenile foliage. Some mature to flat phylodes and you can see the transition stage on some of the lower leaves.
Acacia melanoxylon is a possibility but there's lots of other acacias that have similar foliage. When it has some adult foliage there's a better chance of making an accurate ID.