Fruit tree and Plum tree

Fruit tree noun - Tree bearing edible fruit.

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

Plum tree noun - Any of several trees producing edible oval fruit having a smooth skin and a single hard stone.

Fruit tree and plum tree are semantically related. You can use "Fruit tree" instead a noun phrase "Plum tree".