Office Web App Feature doesn't exist in Site Collection Features

Hi 

I have Installed Office 2010 professional and then SharePoint Server 2010 64 bit and then  Office Web App 2010 .

But After Creating the First Library and try to open office files (work , excel ....) It Cannot open , Only Excel Sheets can be Edited on the the Browser Only .

I have make sure that the services is started , But I try to find Office web apps Feature on site collection feature , but i didn't find it ,

I think that office web app isn't compatible with the sharepoint but i don't know how to get It .

what can I do ? 
Thanks for attention .