It's still a way off, but I've been toying with not even doing a tech tree. From a thematic standpoint I don't it really makes sense. When I think of the bronze age, I think of large palace complexes, expansive trade networks, the first laws, and a devastating collapse. The typical progress-through-technology aspect of Civilization and the like don't fit into that image for me.
Instead I'm thinking of something more akin to the Book of Laws from Frostpunk. Instead of a linear progression, you would be able to specialize your empire through laws. Most laws would offer some form of choice and trade-off. Religion, for example, one of the early laws could be a choice between venerating the gods, or venerating the king. The first choice would lead to a stronger priesthood and temples, the other would lead to a stronger king. Forcing the player to choose between options will cause their empires to evolve and specialize, so that one player could end up radically different than another.
Tech trees in games are often used to gradually ramp-up complexity, helping to ease players into the game. The book of laws wouldn't really do that, so I see a separate progression system based on access to items (such as Mudbrick, Wood, Copper). This system would hide items in the UI until the player has gained access to pre-requisite items. For example, at the start of the game the player wouldn't have discovered mudbrick yet, and so wouldn't see the option to build any structure that requires it (i.e. most of them). But they would be able to construct farms or a brickworks. Once they build a brickworks they'll discover Mudbrick, and gain access to more construction items.
This would move players along a chain of items, and increasing complexity. The end-state could involve a dozen items all linked in intricate production chains, requiring long ranged trade. I think this would be a fairly natural way ease new players into the game, without needlessly slowing down to progress for the player, without locking experienced players behind arbitrary gates. It would also fit thematically, mirroring the complex trade networks at the height of the late bronze age.
Thanks for the post!