By popular request (because Enrico asked)
For a quicker, easier project, it would of course have been possible to just use one of these little dollar store xmas light strings (comes with the 2xAA battery pack and 10 LEDs for about a dollar!).
ps, here is a picture of the battery packs I used for the trees - just the basic cell phone emergency charger types with a USB port providing a nice 5 volts, but very handy to use to make these sorts of projects a bit more mobile, especially for testing. Not sure how long a WiFi WeMos dev board would run on something like this though. The one on the right contains an 18650 Lithium cell, so that might do alright.