These trees are missing from TreeType. They appear in the "Old Growth Spruce Taiga" biome, and I actually remember this going as far back as 1.16, (I forgot to report it then) so these trees have probably been missing from TreeType since their debut in 1.7.10.

The only "mega" taiga tree available within TreeType is the Mega Pine one, which is found in the "Old Growth Pine Taiga" biome. Here's what they look like:

The notable difference between this type of tree is that the leaves are mostly in a pyramid shape at the top, whilst the mega spruce trees have leaves going much further down.

Only the latter tree is available within the TreeType function, so the former is not available anywhere.

Suggested fix: Add a new TreeType called MEGA_SPRUCE that places the former trees shown in the first image.