一个超复杂的xml文档解析

XML code:
<?php
$XMLstr="<DMResponse><Code>1</Code><Description>Your request was successfully received and processed.</Description><ResultData><Explanation> Here is the response to your request </Explanation>
<GetObjectNamesRs>
<ClientTree>
<ClientName>Client_Week</ClientName>
<SiteTree>
<SiteName>SiteMon</SiteName>
<CampaignTree>
<CampaignName>Cam_Mon_Child_0</CampaignName>
<MailingName>Mon__Mailing</MailingName>
<MailingType>StandardMailing</MailingType>
<MailingName>Mon__Mailing_1</MailingName>
<MailingType>StandardMailing</MailingType>
<MailingName>Mon__Mailing_2</MailingName>
<MailingType>StandardMailing</MailingType>
</CampaignTree>
</Sitetree>
<SiteTree>
<SiteName>Site_Week</SiteName>
<CampaignTree>
<CampaignName>Cam_Week</CampaignName>
</CampaignTree>
<CampaignTree>
<CampaignName>Cam_Week_Child_0</CampaignName>
<MailingName>Weekly__Mailing</MailingName>