I've used a 555 timer in a monostable multivibrator configuration to control 4 sets of 4 parallel LEDs that flash in set of 2 rows. Half are connected to the positive voltage and flash once the pin 3 of the timer is low and the others are connected to the negative voltage and flash once the pin 3 i high.
The entire project is powered by a USB power bank.
I recognize that heartbeat "phaser" from Tom's article over the weekend: https://hackaday.com/2018/12/23/arduino-heart-rate-monitor-has-star-trek-chic/
Thanks for making the time-lapse video of assembling three tree, those are always a fun watch and you make it look really easy.