One treaty gives a 10% bonus to your nation's taxable income. The other side gets it too. That's trade.
The other treaty creates a route between the two capitals, and a caravan starts traveling it. It scouts for you, and you get a bonus to relations. You also get a 10% bonus to taxable income to your capital only. That's economy.
The names are confusing.
(I'm editing this answer with everyone's info. Credit goes to Tasunke and Martimus)
It has been suggested that the 10% bonus to the capital taxable income increases as the caravan levels, but I cannot see in a game where I've had 80 turns of peace with a reduced enemy living in a reservation in a corner of the map. If the trade caravans level it takes a while.
