When graphics are set to fancy and I look at one of my trees I only see the front side of the first row of leaves but not any of the leaves blocks behind them, which is not the case for vanilla leaves.

How does this come?

My json files are exactly like the ones for the vanilla leaves and my leaves class extends BlockLeaves so it has all the rendering related methods from there.

If you need to see a specific part of my code, tell me.

Do I need a transparent and a non-transparent or just the non-transparent? And do I need to do anything else?

I did look there and I actually got it to work.