Suppressing groups in a group tree. Bar Chart at run time

[medeya]

Hi All !
I have a web report that takes the information from the user and sends in to the crystal report to change the Top N group selection formula dinamicaly. The parameter sent as a parameter field value, which is a numeric ( N )value for the Top N. The report beeing return shows the topN groups only, but the group tree shows all the groups in the report. Is there a way to suppress the groups in the group tree except for those that are Top N.
And also I need to change the top N value for the chart to display the information for the current Top N group selection.
And I use the report viewer for HTML.

I'd appreciate any help !
Thank you.