In every stage, LEDs are simply wired as a chain and first DIN and last DOU are wired to the inner regiontogether with V+ and GND for later contacting.
The stages are then connected to a 25 LED LED stripe by connection DOUT of the first stage to DIN of the next stage and so on. The tree topper LED is the last one in this chain. V+ and GND connected to every stage. The LEDs are now connected to only one pin of the microcontroller.