This was intended to be a "my first soldering" projects for kids, which sadly did not happen. Here are the files anyway, in the hope that they may be of use.

• R1 and R4: 270 Ω give about 20 mA of current assuming a forward voltage of 2 V for each LED.
• R2 and R3: Values may be varied to change the flashing frequency, but the transistor base current must not be exceeded.
• C1 and C2: Values may be varied to change the flashing frequency. Should be rated for at least 9 V. For ease of assembly, prefer non-polar capacitors.
• LEDs: Any will do, but adjust R1/R4 if needed. The board is designed for 3 mm LEDs. For maximum festiveness, angle the LEDs to resemble electric candles sitting on the tree. In this case, 5 mm LEDs can also be used.
• T1 and T2: Virtually anything NPN will do, just mind the pinout.