Adding rows to Datatable and Binding it ASP.Net GridView

HI, I have a gridview with empty data template.In this empty data template i have a table(HTML) with 4 columns. When user enters data i want to save this in a datatable temprorily at a button click event.. Again if user wants to add one more rows data that also should be added to the same table where i added previous row data. So now the datatable has 2 rows. Like this he may add any no of rows. What i want is all the rows should be displayed when i bind datatable to gridview.. At the click event i am adding 1 row at a time to the datatable