Linq union in c#

public void LinqUnion() 
{ 
    List<Product> products = GetProductList(); 
    List<Customer> customers = GetCustomerList(); 
  
    var productFirstChars = 
        from p in products 
        select p.ProductName[0]; 
    var customerFirstChars = 
        from c in customers 
        select c.CompanyName[0]; 
  
    var uniqueFirstChars = productFirstChars.Union(customerFirstChars); 
  
    Console.WriteLine("Unique first letters from Product names and Customer names:"); 
    foreach (var ch in uniqueFirstChars) 
    { 
        Console.WriteLine(ch); 
    } 
}