typescript type for single and array properties

Question

I have following use case for TypeScript types:

I have a certain interface, e.g:

interface Data {
 a: number;
 b: string;
}

and I need these interfaces:

interface DataSingleValue {
 a: number;
 b: string;
}
interface DataArrayValue {
 a: number[];
 b: string[];
}

So the interfaces do have all properties of the Data-interface with the same data type. Just in one case they are all arrays.

I have a lot of such interfaces and I would like to have something like this:

interface Model<T | T[]> {// dont know how to do}

interface DataSingleValue extends Model<Data> {} --> leads to the same as above
interface DataArrayValue extends Model<Data[]> {} -> leads to the same as above

How to do this?