Shavuos 5778

One reason given why we decorate the shul with greenery is to commemorate Moshe being placed in the Nile in a basket of reeds which occured on Shavuot.

Where did the separate custom of decorating the shul with flowers originate?

Decorating with trees, the concept of חוקת הגוים, and the parameters of חוקת הגוים.

The significance of 3 to Torah and Shavuot.