How can I query the appointed node in XML with XQuery quickly?

The result I hope to get

<Folder Name="Root" Id="a6dce8fe-749c-4e38-ab2f-3d03d9711b3d">
<Folder Name="Card" Id="b8dcf8fe-749c-4e38-ab2f-6d03d9711b8j">
</Folder>
</Folder>

================ Stored In XML field==========================

<Folder Name="Root" Id="a6dce8fe-749c-4e38-ab2f-3d03d9711b3d">
<Bookmark>
<Title>CodeGuru Forums - ASP.NET</Title>
<Url>http://www.codeguru.com/</Url>
<Description>This is a good site</Description>
<InputDate> 2005-12-5</InputDate>
<IsPrivate>False</IsPrivate>
</Bookmark>
<Bookmark>
<Title>We will e-mail your press release</Title>
<Url>http://www.dpdirectory.com/</Url>
<Description>This is a good site</Description>
<InputDate> 2004-12-5</InputDate>
<IsPrivate>False</IsPrivate>
</Bookmark>
<Folder Name="Card" Id="b8dcf8fe-749c-4e38-ab2f-6d03d9711b8j">
<Bookmark>
<Title>Welcome to ePassporte</Title>
<Url>https://www.epassporte.com/</Url>
<Description>Very Good</Description>
<InputDate> 2004-08-5</InputDate>
<IsPrivate>True</IsPrivate>
</Bookmark>
<Bookmark>
<Title>Keystone DreamCard</Title>
<Url>https://www.mydreamcardonline.com</Url>
<Description>Please note</Description>
<InputDate> 2004-08-5</InputDate>
<IsPrivate>True</IsPrivate>
</Bookmark>
</Folder>
</Folder>

=====================================================

Some pepole give me a anwser, It work well, but when the size of the XML field is little big, it run very slowly, could you give a code which can run quickly!

//--Code -
declare @my xml

set @my='
<Folder Name="Root" Id="a6dce8fe-749c-4e38-ab2f-3d03d9711b3d">
<Bookmark BId="f8dce8hj-846c-4e38-ab2f-6d03d9711b80">
<Title>CodeGuru Forums - ASP.NET</Title>
<Url>http://www.codeguru.com/</Url>
<Description>This is a good site</Description>
<InputDate> 2005-12-23</InputDate>
<IsPrivate>False</IsPrivate>
</Bookmark>
<Bookmark BId="fgdce3ak-846c-4e38-ab2f-8i03d9711b23">
<Title>We ll e-mail your press release</Title>
<Url>http://www.dpdirectory.com/</Url>
<Description>This is a good site</Description>
<InputDate> 2004-11-23</InputDate>
<IsPrivate>False</IsPrivate>
</Bookmark>

<Folder Name="Card1" Id="b8dcf8fe-749c-4e38-ab2f-6d03d9711b8j">
<Bookmark BId="ghdce3ak-456c-4e38-ab2f-5h02d9711b67">
<Title>Welcome to ePassporte</Title>
<Url>https://www.epassporte.com/</Url>
<Description>Very Good</Description>
<InputDate> 2004-08-12</InputDate>
<IsPrivate>True</IsPrivate>
</Bookmark>
<Bookmark BId="fkdfh3a8-456c-6y38-jk2f-5h0gh9711b45">
<Title>Keystone DreamCard</Title>
<Url>https://www.mydreamcardonline.com</Url>
<Description>Please note</Description>
<InputDate> 2004-09-25</InputDate>
<IsPrivate>True</IsPrivate>
</Bookmark>

<Folder Name="Card1in1" Id="l9dcf8fe-689c-0935-fghj-7u03d9711b5t">
<Bookmark BId="ghdfh3a8-896c-6y40-jkfg-5h0gh9711b89">
<Title>The News of CNN</Title>
<Url>https://www.cnn.com</Url>
<Description>Please note</Description>
<InputDate> 2004-09-23</InputDate>
<IsPrivate>True</IsPrivate>
</Bookmark>
</Folder>

</Folder>

<Folder Name="Card2" Id="67dcf8fe-734c-4e56-ab2f-6d03d9711bfg">
</Folder>

</Folder>
'

set @my.modify('delete (//*[local-name(.) != "Folder"], //text()) ')

select @my

//--Code-