The Federal Thrift Savings Plan is a public pension plan.
See here for more information from the State of Missouri on this topic. Missouri provides for a public pension exemption from income. In order to be eligible for the full deduction, your Missouri adjusted gross income must fall within certain income limitations. If your income exceeds the limitation, you may qualify for a partial exemption. The amount of your exemption must be reduced by the amount that your income exceeds the limitation. The limitation is based on your filing status and income (less taxable social security benefits) as listed below:
Public pensions are pensions received from any federal, state, or local government. All other retirement income from pensions or IRAs is generally considered private. If you have questions about whether your retirement income is from a public or a private source, contact your retirement plan administrator.
TurboTax will calculate the pension exemption on your Missouri return based on your entries.