One way...

First, insert each of the symbols you want, and create an AutoText entry for
each one. Make the names logical and easy to figure out.

Next, choose Tools - Customize - Categories tab - New Menu category - drage
New Menu command (under Commands:) to the menu and drop it. Right-click the
item and rename it Symbols. If you want a hotkey, I suggest putting & before
the y, e.g., S&ymbols. That way, Alt+Y accesses it.

With the Customize dialog still open, in the Categories tab, click on
AutoText. In Commands, find the first symbol you want to add to the menu.
Drag it to your new Symbols item on the menu--a small blank box opens just
below Symbols. Drop the symbol onto that blank box. Find the next symbol and
drag it to above to below the one you just dropped -- alphabetic order is
probably not a bad organization scheme. Repeat this until you're done, and
click Close.