def make_multiallelic_alts(records):
    """
    Make list of alts corresponding to record with highest observed copy number

    Parameters
    ----------
    records : list of pysam.VariantRecord

    Returns
    -------
    alts : tuple of str
    """
    
    max_CN = 2

    is_bca = records[0].info['SVTYPE'] not in 'DEL DUP'.split()

    for record in records:
        if record.alts[0] == '<CN0>':
            CN = int(record.alts[-1].strip('<CN>'))
            if CN > max_CN:
                max_CN = CN

    if is_bca:
        return tuple(['<CN1>'] + ['<CN%d>' % i for i in range(1, max_CN + 1)])
    else:
        return tuple(['<CN0>'] + ['<CN%d>' % i for i in range(1, max_CN + 1)])