Can't put all generated classes in a single file

Can't find how to generate classes inside a single file. 

For example
```
{
  "bars": [
      {
        "barz": "string"
      }
  ]
}
```

would create this file: 
```
data class Foo(
  val bars: List<Bar>
)

data class Bar(
  val barz: String
)
```