列表的分类问题

a=[[“50063964”, “3.00”, “UNS -16402-021”, “25AZ7026”], [“50063964”, “1.00”, “UNS -23050-045”, “1DBK2223”],
[“50063965”, “3.00”, “UVS -16023-112”, “21QB3011”], [“50063965”, “1.00”, “FDN-25363-010”, “2FRC3011”],
[“50063966”,“1.00”,‘null’, ‘null’],[“50063966”,“3.00”,‘null’,‘null’],
[“500639677”,“3.00”,‘null’,‘null’],
[“500898979”,“5.0”,‘000’,‘00’]]
如何把二位列表,不使用其他库,仅仅使用逻辑来分类,按照第一个元素代码分类数据,分类变成三维列表:
b = [[[“50063964”, “3.00”, “UNS -16402-021”, “25AZ7026”], [“50063964”, “1.00”, “UNS -23050-045”, “1DBK2223”]],[[“50063965”, “3.00”, “UVS -16023-112”, “21QB3011”], [“50063965”, “1.00”, “FDN-25363-010”, “2FRC3011”]],[[“50063966”,“1.00”,‘null’, ‘null’[“50063966”,“3.00”,‘null’,‘null’]],[
[“500639677”,“3.00”,‘null’,‘null’]],[
[“500898979”,“5.0”,‘000’,‘00’]
]
]