XSLT- Create a tree from XML

I want to create an XML with a hierarchic structure from a flat XML file. The XML file contains the parent-child relations and if a node is a leaf or not.

There is no explicit information about the level of nesting or the root nodes in the structure. The XML-file can contain more than one root element and it is not ordered.

<list>
<stru><parent>A01</parent><child>P04</child></stru>
<stru><parent>B11</parent><child>P01</child></stru>
<stru><parent>B12</parent><child>P01</child></stru>
<stru><parent>B12</parent><child>P03</child></stru>
<stru><parent>B21</parent><child>P02</child></stru>
<stru><parent>B21</parent><child>P03</child></stru>
<item><cod>B01</cod><isparent>Y</isparent></item>
<item><cod>B11</cod><isparent>Y</isparent></item>
<item><cod>B12</cod><isparent>Y</isparent></item>
<item><cod>B21</cod><isparent>Y</isparent></item>
<item><cod>P01</cod><isparent>N</isparent></item>
<item><cod>P02</cod><isparent>N</isparent></item>
<item><cod>P03</cod><isparent>N</isparent></item>
<item><cod>A01</cod><isparent>Y</isparent></item>
<item><cod>P04</cod><isparent>N</isparent></item>
<stru><parent>B01</parent><child>B11</child></stru>
<stru><parent>B01</parent><child>B12</child></stru>
<stru><parent>B11</parent><child>B21</child></stru>
</list>

The needed result is shown below. I don't know how to do this.

I found a transformation that creates that structure if the root node is known.

<list>
    <itemlist>
        <item>
            <cod>A01</cod>
            <itemlist>
                <item>
                    <cod>P04</cod>
                </item>
            </itemlist>
        </item>
        <item>              
            <cod>B01</cod>
            <itemlist>
                <item>
                    <cod>B11</cod>
                    <itemlist>
                        <item>
                            <cod>B21</cod>
                            <itemlist>
                                <item>
                                    <cod>P02</cod>
                                </item>
                                <item>
                                    <cod>P03</cod>
                                </item>
                            </itemlist> 
                        </item>
                        <item>
                            <cod>P01</cod>
                        </item>
                    </itemlist>
                </item>
                <item>
                    <cod>B12</cod>
                    <itemlist>
                        <item>
                            <cod>P01</cod>
                        </item> 
                        <item>
                            <cod>P02</cod>
                        </item> 
                    </itemlist> 
                </item>
            </itemlist>
        </item>
    </itemlist>
</list>