Rather than a single sapling that grows either into Bloody Spruces or Vampire Spruces depending of the soil it was planted, there should be saplings for both types of trees. The reason is: the sapling that grows into both trees is named after only one of the resulting trees, wich is the Bloody Spruce; and the Vampire Spruces can only be grown when planted in regular dirt, even though they generate in Vampire Forests, wich have a ground mainly made of Cursed Soil, so it doesn't makes sense for them to generate there. Therefore, the addition of separate saplings for both trees would fix this inconsistency.

Should be fixed for 1.17+.
For 1.16 Vampirism 1.9 will change the trees anyways