I made some headway today, and was able to wire up one of the XMas trees to one of the Wemos boards.
Initial testing went well - it looks like the lights are properly controlled the way I had intended (hooray!).
However, the motion sensor is not doing the right thing yet, so I'll have to work on that.
edit: I think I might have found the issue (will test tomorrow) - line 77 sets the motion sensor input as "INPUT_PULLUP" like a regular button, but the PIR module should already handle that, so it probably should just be "INPUT". edit again: Sadly that wasn't the problem. I'll test it separately later.
I have the wires and the transistors just soldered together dead-bug style to keep things simple.
Once it all works I'll give the exposed bits a nice coat of... you guessed it... nail polish!
And then I need to somehow tuck the wires and board into a neat little finished package.
I made a little video showing my progress so far.
I'm using a Witty Wifi as the other tree. pressing the button simulates the motion detected, and the different LEDs simulate the tree.
Sorry about the video, I took it in portrait mode LIKE A BARBARIAN! (no offence intended to barbarians).
Here is a screenshot that shows the online MQTT client I also used for testing. It's super handy for this kind of thing!
You can see the debug info in the serial console too.
Since it looks like the software is ok for the most part (it may need a tweak for the motion detector), I've published it on GitHub, including the version that runs on the Witty for testing.