Tasks in C# are executing sequentially and not concurrently

Question

For purely experimental reasons, I am trying to write a psuedo-random number generator using Tasks in C#

I have 2 tasks, and 2 static variables glo_a and glo_count. glo_a is supposed to hold the final result (a 7-bit random binary integer).

public static int glo_a = 0, glo_count = 6;

Private void button1_Click(object sender, RoutedEventArgs e)
{
  Task task = new Task(() => this.display(1));
  Task task2 = new Task(() => this.display(0));

  task.Start();
  task2.Start();

  Task.WaitAll();
  textBox1.AppendText("\n" + glo_a);
}

public void display(int j)
{
  for (; glo_count >= 0; glo_count--)
  {  
    glo_a += j * (int)Math.Pow(10,glo_count);
  }
}

private void refreshbutton_Click(object sender, RoutedEventArgs e)
{
  /* reset the original values*/  
  glo_a = 0;
  glo_count = 6;
  textBox1.Text = "";  
}

The problem I'm having is that task executes first and completes before task2 begins every single time.