@classmethod
def to_pandas(indices):
    if isinstance(indices[0], pd.RangeIndex):
        merged = indices[0]
        for index in indices[1:]:
            merged = merged.union(index)
        return merged
    else:
        return indices[0].append(indices[1:])
@classmethod
def to_pandas(indices):
    if isinstance(indices[0], pd.RangeIndex):
        merged = indices[0]
        for index in indices[1:]:
            merged = merged.union(index)
        return merged
    else:
        return indices[0].append(indices[1:])