How to import a output trace file from NS2 to excel?

There is no ready made converter available to convert ns-2 event trace files in to Excel files.

But,  you can use space as delimit and import the ns-2 trace files (.tr files) in to Excel and then manually remove unwanted columns and rows.

But, it is not adviceable since there are LOT of freely available tcl, awk, perl, python and shell scripts available to do trace analysis in a more meaningful and logical way.