Okay kiddo, let's imagine you have a lot of toys that you really like and your friend has some toys too. You both really want some of each other's toys and you decide to make a deal. A commercial treaty is kind of like that deal, but with countries instead of friends and things that they want to trade with each other.
So, let's say that your country, Country A, makes a lot of really good chocolate and your friend's country, Country B, makes really good cheese. Country A really wants some cheese and Country B really wants some chocolate, but they don't want to pay too much for it.
That's where the commercial treaty comes in. The leaders of both countries will talk to each other and come up with a plan. They might agree to lower the taxes (also called tariffs) that they usually charge on imported goods, which makes it cheaper for people in Country A to buy cheese from Country B and cheaper for people in Country B to buy chocolate from Country A.
This can be really good for both countries because it helps their companies sell more stuff and make more money. This can also lead to more jobs in both countries because the companies need people to make and sell the things they are trading.
So, a commercial treaty is kind of like a deal between two countries to help them trade things they want with each other and make it easier and cheaper for people to buy and sell those things.