Is it possible to

[opaque torrent]

Change ALL trees to oak trees?

[idle hatch]

Yes

You need to change surface tree feature rules of all biomes to oak tree

[hybrid bloom]

Do you want a clear explanation?@opaque torrent

[opaque torrent]

Ye

[hybrid bloom]

First you need the structure of the tree

[opaque torrent]

Ok

[hybrid bloom]

Then you need to create a feature like this for every tree

[opaque torrent]

Oh, I'd expect that

Lol

[hybrid bloom]

In my case is had 5 trees so I created 5 feature

Then you need to create a feature like this

Next we need tree feature of the biome in my case forest . Get the tree feature from minecraft

Do you understand?

BTW don't forget to add void blocks in structure

Then we need feature rule

Get the feature rule of the biome in my case it's forest so take it mostly all biome will have this name

(Biome_name)_surface_trees_feature

Don't change the name of the feature rule

And finally you need this feature rule

You can get this also

From the minecraft files

Can you understand if you need help ask me

[neat hedge]

if you finish making this mcpack please post it i'd love to give it a quick whirl

[hybrid bloom]

Who?