私は持っている
XmlElement root;
このような構造を含む
<?xml version="1.0" encoding="us-ascii"?>
<EntityCollection xmlns="">
    <Application xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
        <id>C</id>
        <CDate>2010-06-29T00:00:00</CDate>
        <Applicants>
            <PersonID>1</PersonID>     
            <Age>4651</Age>
            <IncomeCollection>
                <Amount>20</Amount>
                <Frequency>W</Frequency>
            </IncomeCollection>
        </Applicants>
        <Applicants>
            <PersonID>15</PersonID>     
            <Age>4651</Age>
            <IncomeCollection>
                <Amount>20</Amount>
                <Frequency>W</Frequency>
            </IncomeCollection>
        </Applicants>
        <Applicants>
            <PersonID>6</PersonID>     
            <Age>4651</Age>
            <IncomeCollection>
                <Amount>20</Amount>
                <Frequency>W</Frequency>
            </IncomeCollection>
        </Applicants>
        <tag>N</tag>
    </Application>
</EntityCollection>
結果が以下のようになるように、応募者を PersonID で並べ替えたい:
<?xml version="1.0" encoding="us-ascii"?>
<EntityCollection xmlns="">
    <Application xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
        <id>C</id>
        <CDate>2010-06-29T00:00:00</CDate>
        <Applicants>
            <PersonID>1</PersonID>     
            <Age>4651</Age>
            <IncomeCollection>
                <Amount>20</Amount>
                <Frequency>W</Frequency>
            </IncomeCollection>
        </Applicants>
        <Applicants>
            <PersonID>6</PersonID>     
            <Age>4651</Age>
            <IncomeCollection>
                <Amount>20</Amount>
                <Frequency>W</Frequency>
            </IncomeCollection>
        </Applicants>
        <Applicants>
            <PersonID>15</PersonID>     
            <Age>4651</Age>
            <IncomeCollection>
                <Amount>20</Amount>
                <Frequency>W</Frequency>
            </IncomeCollection>
        </Applicants>
        <tag>N</tag>
    </Application>
</EntityCollection>