A federal State is a complex organisation. It requires that there should be a double mode of representation; one for the country as a whole anr1 another for the component units as such. It therefore requires two chambers. Moreover, the component units may differ in size, population and resources.
Yet the principle of equality-or parity requires that they should have the same voice and equal representation in the federal government. In view of these requirements, a federal legislature consists of two Houses, one of which represents the nation as a whole, while the other represents the component units on an equal basis.
That is the-reason why bicameralism is a necessary feature of the federation.