With the Tree style, each element node is an array. The first member is the name of that element, the second is a reference to an array (the content of that element). The first item of that array is a hash reference which contains any attributes (or nothing, if there are none). The data structure looks something like this:

[ "outside",
    [ "inside",
        [ { "name" => "Wibble"},
         0, "some data"]
    ]
]
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Yuck.