php / mongoDB：将项添加到内部数组

My structure looks like this:

我的结构看起来像这样:

"_id" : { "$oid" : "502ac2858386b3f419000002"} ,
"eventName" : "eventA" ,
"eventStreamName" : "eventA-0001" ,
"encoders" : [ 
    { 
    "encoderName" : "enc-201" ,
    "streams" : [ 
        { "language" : "eng" , "format" : "flash" , "priority" : "primary"} ,
        { "language" : "spa" , "format" : "flash" , "priority" : "primary"} ,
        { "language" : "fra" , "format" : "flash" , "priority" : "primary"}
        ]
    } ,
    { 
    "encoderName" : "enc-202" ,
    "streams" : [ 
        { "language" : "eng" , "format" : "flash" , "priority" : "primary"} ,
        { "language" : "spa" , "format" : "flash" , "priority" : "primary"}   // i'd like to add stream here
        ]
    } 
]
"