combining multiple xml files

I am wanting to combine multiple xml files looking as follows:

File 1:

<class>
              <id>001</id>
              <name>beginning</name>
        <section>
                <id>100</id>
                <name>Anderson</name>
                <detail>some text</detail>
        </section>
</class>

File 2:

<class>
        <id>001</id>
        <name>beginning</name>
        <section>
                <id>100</id>
                <name>Anderson</name>
                <detail>some more text</detail>
        </section>
</class>

File 3:

<class>
        <id>001</id>
        <name>beginning</name>
        <section>
                <id>200</id>
                <name>Anderson</name>
                <detail>more text</detail>
        </section>
</class>

File 4:

<class>
        <id>002</id>
        <name>advanced</name>
        <section>
                <id>100</id>
                <name>Jones</name>
                <detail>some final text</detail>
        </section>
</class>

and have the output look as such...any suggestions?

<output>
        <class>
                <id>001</id>
                <name>beginning</name>
                <section>
                        <id>100</id>
                        <name>Anderson</name>
                        <detail>some text</detail>
                        <detail>some more text</detail>
                </section>
                <section>
                        <id>200</id>
                        <name>Anderson</name>
                        <detail>more text</detail>
                </section>
        </class>
        <class>
                <id>002</id>
                <name>advanced</name>
                <section>
                        <id>100</id>
                        <name>Jones</name>
                        <detail>some final text</detail>
                </section>
        </class>
</output>

Thanks

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