Hi krPreistoric and welcome to the forum!
This is the section of code responsible for spawning wild bee hives into the world. The server will check once every 800 seconds (or about 13 minutes) for leaves loaded in the same block (aka "chunk) that a player is in. You can see that it does this check on
group:leaves that are neighboring air nodes.
There is a 1 in 10 chance of it running its function. If it does run it, it runs the
action = section of the code.
If you look at that section, If it does run, it'll do some other stuff that deals with elevation and positioning, and checks the elevation of the leaves. Then it runs a check for 'group:flora`, which are typically flowers. If it finds a match, it adds a wild bee have.
So to summarize, you need to have leaves that are up above the ground, that are near air, with flowers around / underneath. They are not set to be biome specific so even though you live near jungle, they should still spawn.
If you want to explore the source code a bit more, you can find it here. I run an edited version of this mod. I'll eventually publish all the source code for mods to a notabug.