bulbs

Put ammeters in series with the circuit branches and you will see why. The top lamp is passing more current. Can you see why?

Lamps work as a type of resistor. When you put two or more in series as you've done to the left of the top lamp---you increase the total resistance. When you pot two or more in parallel as you did to the right of the top lamp---you decrease resistance. Therefore, the left branch resists more current then the right. After summing the equivalent resistances you have two lights on the left but only one and a half lights on the right. The top most lamp is on the right hand branch which takes more current then the left, and all of that current passes through the top lamp making it twice as bright as the other two lamps on the right which each only get half of the current of the top bulb. The two lamps on the right branch each get the same amount of current making them the same brightness as each other but since the current is less then the left side neither bulb is as bright as the top one.

Oh, and your circuit has lamps (incandescent bulbs) instead of LEDs. If you used LEDs with a resistor to limit the current, they could all be the same brightness.