Says it all on the tin I think

For example, meditation around fire can help progress the conflagrator tree


Another direction this could go is to lock certain trees behind their related foci

For example, you can only unlock and progress the conflagrator tree by meditating around fire


On an unrelated note, I think it'd be cool if the 'extinguish fire' psycast, instead creating a firefoam explosion, would absorb all flames near the psycaster granting them psyfocus and neural heat based on the amount of fire consumed.