Birch tree and White birch

Birch tree noun - Any betulaceous tree or shrub of the genus Betula having a thin peeling bark.

White birch and birch tree are semantically related. In some cases you can replace phrase "White birch" with "Birch tree", this phrases are similar.

White birch noun - European birch with dull white to pale brown bark and somewhat drooping hairy branches.

Birch tree and white birch are semantically related. You can use "Birch tree" instead a noun phrase "White birch".