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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def from_(cls, gsim):
 """ Generate a trivial GsimLogicTree from a single GSIM instance. """

        ltbranch = N('logicTreeBranch', {'branchID': 'b1'},
                     nodes=[N('uncertaintyModel', text=str(gsim)),
                            N('uncertaintyWeight', text='1.0')])
        lt = N('logicTree', {'logicTreeID': 'lt1'},
               nodes=[N('logicTreeBranchingLevel', {'branchingLevelID': 'bl1'},
                        nodes=[N('logicTreeBranchSet',
                                 {'applyToTectonicRegionType': '*',
                                  'branchSetID': 'bs1',
                                  'uncertaintyType': 'gmpeModel'},
                                 nodes=[ltbranch])])])
        return cls(repr(gsim), ['*'], ltnode=lt)