sub menu height is become problem

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C#

ASP.NET

Hello friends,

I'm developing a web application, in that a i'm using a menu control in asp.net c#.
it is working fine for smaller sub-menus like the count of menu items less than 20-25, but when the item size increases then it behaves like drop down list which is starting from the top of screen to bottom.

Is there any way to over come this means staring submenu next down to the main menu item and it may go down without drop down list

Please help me out to get rid of this problem
thank you