If by individual LEDs you definitely mean individual and not runs of 3 LEDs, then I would:

- flash WLED onto an ESP8266

- solder a data output and power lines to the LED strip

- go through the list of LED options in WLED until one worked

- try displaying Red, Green, and Blue to confirm that the RGB order was right

It would be pretty rare (I guess) to find a tree that was using a truly custom addressable LED strip with its own protocol