Complex sentence: Recently Sreedharan was appointed by the UN Secretary General Ban Ki-moon to serve on the United Nations's High Level Advisory Group on Sustainable Transport (HLAG-ST) for a period of three years.
Split into simpler sentences: Recently Sreedharan was appointed to serve the United Nations's High Level Advisory Group on Sustainable Transport (HLAG-ST). He was invited by UN Secretary General Ban Ki-moon to serve on his HLAG-ST for a period of three years.