How to move item from ListBox to another

Create new page and add two ListBox (lstEmployees ,lstSelectedEmployees) and in lstEmployees ListBox add items and the other one don't
also add four buttons (btn_Add , btn_Remove ,btn_AddAll ,btn_RemoveAll)

In Default.aspx.cs

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class Default2 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}

protected void btn_Add_Click(object sender, EventArgs e)
{
if (lstEmployees.SelectedIndex > -1)
{
string _value = lstEmployees.SelectedItem.Value; //Gets the value of items in list.
string _text = lstEmployees.SelectedItem.Text; // Gets the Text of items in the list.
ListItem item = new ListItem(); //create a list item
item.Text = _text; //Assign the values to list item
item.Value = _value;
lstSelectedEmployees.Items.Add(item); //Add the list item to the selected list of employees
lstEmployees.Items.Remove(item); //Remove the details from employee list


}
}

protected void btn_Remove_Click(object sender, EventArgs e)
{
if (lstSelectedEmployees.SelectedIndex > -1)
{
string _value = lstSelectedEmployees.SelectedItem.Value; //Gets the value of items in list.
string _text = lstSelectedEmployees.SelectedItem.Text; // Gets the Text of items in the list.
ListItem item = new ListItem(); //create a list item
item.Text = _text; //Assign the values to list item
item.Value = _value;
lstSelectedEmployees.Items.Remove(item); //Remove from the selected list
lstEmployees.Items.Add(item); //Add in the Employee list

}

}

protected void btn_AddAll_Click(object sender, EventArgs e)
{
int _count = lstEmployees.Items.Count;
if (_count != 0)
{
for (int i = 0; i < _count; i++)
{
ListItem item = new ListItem();
item.Text = lstEmployees.Items[i].Text;
item.Value = lstEmployees.Items[i].Value;
//Add the item to selected employee list
lstSelectedEmployees.Items.Add(item);
}

}

//clear employee list
lstEmployees.Items.Clear();


}

protected void btn_RemoveAll_Click(object sender, EventArgs e)
{
int _count = lstSelectedEmployees.Items.Count;
if (_count != 0)
{
for (int i = 0; i < _count; i++)
{
ListItem item = new ListItem();
item.Text = lstSelectedEmployees.Items[i].Text;
item.Value = lstSelectedEmployees.Items[i].Value;
lstEmployees.Items.Add(item);
}
}

lstSelectedEmployees.Items.Clear();//clear the items
}
}