How can I add more than one vanilla structure to a custom dimension?

I'm wondering how I can add more than one vanilla structure to my custom dimension. Whenever I try to add another structure the dimension breaks.

This is located at the bottom of the json file. I can change it to be any structure but I cant seem to add another structure onto it. (yes I have tried adding an extra bracket when I tried adding a second structure)

      "structures": {
        "structures": {
          "minecraft:village": {
            "spacing": 50,
            "separation": 5,
            "salt": 0
          }
        }
      }