C# Wpf DataGrid variable number of columns

I want to make a datagrid with a varaible number of colums, which set after the config file is loaded. Like the example from wpf-tutorial but with variable number of extra atributes as array but this is not working:

    using System;
using System.Collections.Generic;
using System.Windows;

namespace WpfTutorialSamples.DataGrid_control
{
    public partial class DataGridColumnsSample : Window
    {
        public DataGridColumnsSample()
        {
            InitializeComponent();

            List<User> users = new List<User>();
            users.Add(new User() { Id = 1, Name = "John Doe", Birthday = new DateTime(1971, 7, 23),ExtraAttribute=new int[4] });
            users.Add(new User() { Id = 2, Name = "Jane Doe", Birthday = new DateTime(1974, 1, 17) ,ExtraAttribute=new int[4]});
            users.Add(new User() { Id = 3, Name = "Sammy Doe", Birthday = new DateTime(1991, 9, 2),ExtraAttribute=new int[4] });

            dgUsers.ItemsSource = users;
        }
    }

    public class User
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public DateTime Birthday { get; set; }
        
        public int[] ExtraAtribute {get;set}

    }
}