[1.12] Randomize custom villager trades

Hello!

I'm working on making a custom villager that sells stuff from my mod. I'm giving him trades by using VillagerCareer#addTrade(int level, ITradeList tradelist)

However, this basically says when you trade a level 1 thing, you unlock everything in level2, and so on. Is there a way of getting him to only have some trades per level?

For example, villager lvl1 can buy wool for 1 emerald, buy string for 1 emerald, buy flesh for 1 emerald, then level 2 can buy gold for 1 emerald, can buy fish for 1 emerald.

Currently, my villager would automatically have every level 1 trade, then if u trade once, it unlocks everytrade for level2, Instead I want to see it have something like buy wool for 1 emerald, buy string for 1 emerald, then unlocks buy gold for 1 emerald only, and then go on to unlock level3 trades, etc.

Thanks!