There are some great discussions on sizing wires if you do a quick search of this forum. I recommend you read up a bit-understanding electrical and the basic precautions (like fusing) is a good skill and may keep your bus from going up like a roman candle.
You'll need to size the wire running the length of the bus to support the current, as well as ensure the voltage drop to the last puck light is not noticeable.
If you have ten puck lights (and I'm assuming you're using LED-type), a quick check of Amazon indicates they are about .2 amps apiece at 12VDC. My experience is voltage drop is not much of a problem with these lights-they don't dim appreciable until you're down to about 7-8VDC, so you have some latitude.
The minimum wire gauge for a 2 amp load is 18 gauge, however you'd probably notice the dimming at the end of the run due to voltage drop. To keep the voltage drop reasonable over 25 feet (I see you have a shortie) when I look up a 2 amp load, 50' run (there and back again), a 14 gauge wire will give you about a half a volt drop-very much acceptable, and should not be noticeable on the pucks at the end of the run.
If you plan to branch horizontally off that main run to feed individual pucks, that wire can be smaller because the load is only .2 amps. I'd probably use 18 gauge there.
Please make sure you know the amp draw of your pucks. And if you're burying the wiring behind some beautiful ceiling finish, I'd definitely mock up the system before installing to ensure the visual result is what you hope it will be.