Already doing level gating, why not let people spend their points in as many trees as they want? Then people can stop debating whether 5 twists is better than 3 trees. The fixed EDP is plenty of gravity to keep it grounded.
Feeling like you'd have to be too stingy with Tier 1 then? No, stop it! Just don't make it even worse and let people have as many trees as they want. Super simple actually.