How to convert sublists to a flat list using LINQ in C#

In C#, I have a list as below :

public class Brand{
   public string Name {get; set;}
   public List<string> Models {get; set}
}

Now I want to get all value from Models properties and push it into a list variable.

I tried using LinQ with Select() method as below but it does not work for me.

List<Brand> lstBrands = _brandBo.GetList();
List<string> lstModel = lstBrands.Select(x => x.Model.Select(y => y).ToList()).ToList();

lstModel always return a nested list. Thanks for any solution.