code: def from_(cls, gsim):
          
          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)
docs: Generate a trivial GsimLogicTree from a single GSIM instance.