You need to add 10ml of base. The nicotine strength and PG/VG composition of the base will contribute to the end result. Here are some examples:
50ml Shortfill e-liquid + 10ml base 0mg/ml nicotine = 60ml e-liquid with 0mg/ml nicotine.
Shake and Vape (50ml) e-liquid + 10ml base 9mg/ml nicotine = 60ml e-liquid with 1.5mg/ml nicotine.
S&V with 50ml e-liquid + 10ml base 18mg/ml nicotine = 60ml e-liquid with 3mg/ml nicotine.
You can find more information in the section Shortfill (Shake and Vape) and Nicotine Calculator and Shortfill (Shake and Vape) and PG/VG Calculator.