Tax on NPS Tier 2 amount withdrawl

The withdrawal of the amount in the NPS tier 2 account is taxable. So how this tax is calculated? 

1) Should I treat it as capital gain and do tax calculation on the gain considering it as an equity mutual fund (as my major contribution is on equity)?

2) or should I consider the tax considering it as a part of the income. So in this scenario do I have to pay tax only on the interest earned or on the whole money withdrawal (as the tax on the invested money is already considered in the previous investment year so why to pay tax on the same amount twice)?