Charcoal, 26 bytes
UO⁵¦⁴/‖M↓→‖M↓→‖M‖BO²⁰‖BO↓⁸
Try it online! Link is to verbose version of code.
Explanation:
UO⁵¦⁴/ - drawing a 5 by 4 rectangle filled with /
‖M↓→ - reflect and mirror the canvas to the down and leftright directdirection (note that doesn'tfor matterthis whichpattern youorder dodoesn't firstmatter)
‖M - reflect mirror without a argument (default is to the right, n times)
‖BO²⁰ - reflect butterfly overlap which would reflect the same thing 20n times to the left by default
‖BO↓⁸ - 8 characters but this time with a given direction which is down
Optimizing: -9, Thanks to @Neil for the help on reflects.