As per the subject:

+To clarify the biomes:
+Giant Tree Tiaga: 2x2 Giant Spruce trees with leaves at top of tree
Giant Spruce Tiagre: Almost same as Giant Tree Tiaga except the Giant Spruce trees have leaves covering most of trunk...

Only reason I discovered this was because I wanted to build bases in both biomes but could hardly tell the difference in the biomes as there were Giant Spruces (leaves covering trunk) in the Giant Tree Tiaga (leaves on top only) biome and Giant Trees (top leaves) in Giant Spruce Tiaga (leaves on trunk) biomes. I also checked the hills variants and same issue was found.

If the game is coded to have both variants of tree in BOTH biomes but the incidence is higher for the biome specific tree then please disregard this ticket (I cant even understand what I wrote here either smh)