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A Lie Group which has a simply connected covering group Homeomorphic to 
.  The prototype is any
connected closed subgroup of upper triangular Complex matrices with 1s on the diagonal.  The
Heisenberg Group is such a group.
References
Knapp, A. W.  ``Group Representations and Harmonic Analysis, Part II.''  Not. Amer. Math. Soc. 43, 537-549, 1996.