The rate tree can be created by following these steps:
Observe the current interest rate of the relevant security (bond or derivative).
Determine the probability of the interest rate either going up or down. In most cases, the risk-neutral probability (i.e., the probability of future outcomes adjusted for risk) is used to calculate the future interest rate. Note that if the probability of the interest rate increase equals p, the probability of the interest rate decrease equals (1-p). In addition, the risk-neutral probability can be used for calculating the future rates in all time periods.
Calculate the forward (future) rates using the determined probability.
Create the binomial tree using the obtained interest rates.