Saving ttf file

How can I save Masters together , after saving file it shows 2 different font 1st is Regular and 2nd is Bold . pls help

A .glyphs file can contain multiple masters.

A .ttf file can only contain a single font, so Glyphs will export multiple .ttf font files if you have multiple font styles (as defined in the Exports tab in the Font Info window of Glyphs).