The government of the TDR is federal and comprises two layers and three branches. The first layer is the federal administration within which there are the executive, judicial and legislative bodies. The legislative body, the Congress, wields the most power and is bicameral, including both a House of Representatives and a Senate.
Whilst the Terran government retains the name of the United Nations, it has evolved far beyond the original structure, having abandoned Security Councils and General Assemblies in the late 21st century in favour of the federal presidential system which worked so well in the United States of America. The reasons for this are that the original United Nations was meant as a supplement to national identity, rather than a world government in its own right. Since the unification of Earth, the need for a functioning world government became paramount, and since the original United Nations was tantamount to a failure, its structure changed in everything but name, adapting parts of the presidential and parliamentary system.
The second layer of government is the United Nations Planetary Governments. Answerable to the federal administration, and required to carry out the laws enacted by the federal government, the Planetary Governments do have a certain degree of autonomy with local legislation.