detect the pressing of 220v push button by MCU
You may want to consider debouncing the signal to the MCU with a capacitor in parallel with the resistor. I would simply recommend a 10K resistor and then experiment to figure out a good cap value to go with it. Debouncing can also be performed by software in some cases.

Otherwise, depending on what you plan to do with the signal from the relay, the MCU may experience multiple rising or falling edges even though the relay has only been "turned on" once.

You may find this thread on choosing pull resistors and this thread on debouncing buttons helpful.