Add events from gmail to google calendar

This email received from my
let me confirm my appointment,
give me direction from google map to the dental office,
also let me to add to my google calendat.
Well,  this "add to calendar" icon failed to automatically add event to calendar
instead its downloaded as an .ics file.
To make thing worse,
from google calendar import event setting, (options:settings:import calendar)
I cannot process this event into google calendar,(I do not use outlook either)
All its telling is "Processed zero events"
Seems like most vendor of web calendar dont have agreements on the format of calendar yet.

Dirty trick:
Highlight the day, time and event,  do a quick add to  mini calendar on the left panel.
google calendar insert it to the right timing slot for you.