Hi ashishsuman4u ,
We had a test on our local by using your code and the sitemap, but we did not repro your problem. But when we opened the webpage by IE, www.thanksadpx.com , we noticed there is some javascript error at the foot of the browser.
So, maybe the javascript cause your problem, or it's you css, you can try to remove the class of the divs : <div id="wrapper"> and <div id="header">, in order to see whether the submenu can display.
Hope it helps.
Please remember to mark the replies as answers if they help and unmark them if they provide no help.
Yours sincerely,
Amanda Wang
Microsoft Online Community Support