[WPF] Поиск по ListBox, с использованием TextBox и Button

class Employee
{
  public int EmpNo { get; set; }
  public string EmpName { get; set; }
}

<Grid>
<ListBox Height="298" HorizontalAlignment="Left" Margin="80,55,0,0"
Name="lstEmpData" VerticalAlignment="Top" Width="252">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding EmpName}"></TextBlock>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<TextBlock Height="23" HorizontalAlignment="Left" Margin="60,18,0,0"
Name="textBlock1" Text="Search Name"
VerticalAlignment="Top" Width="134" />
<TextBox Height="27" HorizontalAlignment="Left" Margin="208,13,0,0"
Name="txtNameToSearch" TextChanged="txtNameToSearch_TextChanged"
VerticalAlignment="Top" Width="202" />
</Grid>

ObservableCollection<Employee> lstEmployee =
new ObservableCollection<Employee>();

private void Window_Loaded(object sender, RoutedEventArgs e)
{
lstEmployee.Add(new Employee() { EmpNo = 1001, EmpName = "Mahesh" });
lstEmployee.Add(new Employee() { EmpNo = 1002, EmpName = "Amit" });
lstEmployee.Add(new Employee() { EmpNo = 1003, EmpName = "Vaibhav" });
lstEmployee.Add(new Employee() { EmpNo = 1004, EmpName = "Ashwin" });
lstEmployee.Add(new Employee() { EmpNo = 1005, EmpName = "Prashant" });
lstEmployee.Add(new Employee() { EmpNo = 1006, EmpName = "Vinit" });
lstEmployee.Add(new Employee() { EmpNo = 1007, EmpName = "Abhijit" });
lstEmployee.Add(new Employee() { EmpNo = 1008, EmpName = "Pankaj" });
lstEmployee.Add(new Employee() { EmpNo = 1009, EmpName = "Kaustubh" });
lstEmployee.Add(new Employee() { EmpNo = 1010, EmpName = "Mohan" });
 
lstEmpData.ItemsSource = lstEmployee;
}

private void txtNameToSearch_TextChanged(object sender,
TextChangedEventArgs e)
{
  string txtOrig = txtNameToSearch.Text;
  string upper = txtOrig.ToUpper();
  string lower = txtOrig.ToLower();
 
  var empFiltered = from Emp in lstEmployee
  let ename = Emp.EmpName
  where
   ename.StartsWith(lower)
   || ename.StartsWith(upper)
   || ename.Contains(txtOrig)
   select Emp;
 
  lstEmpData.ItemsSource = empFiltered;
}