One of the quickest solution I would suggest is that put the below code on every page load and replace "Home" with every page name.
Note: There could be many other ways of doing this... One of the quickest way is server side coding as you have only 6 pages.
if (!IsPostBack)
{
Menu M = (Menu)this.Master.FindControl("NavigationMenu");
foreach (MenuItem item in M.Items)
{
if (item.Text == "Home")
{
item.Selected = true;
}
}
}