PHP creates XML and formats output

PHP creates XML and formats output
DOMDocument create XML, set $dom->formatoutput = True, but only the first level node under the root node is created, and the child nodes under the first level node are not (Figure 1). What I want is that the entire XML file is formatted output (Figure 2)
Figure 1:

Figure 2:

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------Solution--------------------
Your code, stick it out.
------Solution--------------------
Use tidy
This is the Html/xml Gospel, take a moment to understand it is worth it

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