Fruit tree and Nectarine tree

Fruit tree noun - Tree bearing edible fruit.

Nectarine tree and fruit tree are semantically related. In some cases you can replace phrase "Nectarine tree" with "Fruit tree", this phrases are similar.

Nectarine tree noun - Variety or mutation of the peach bearing fruit with smooth skin and (usually) yellow flesh.

Fruit tree and nectarine tree are semantically related. You can use "Fruit tree" instead a noun phrase "Nectarine tree".