You need to encode the XML tags for the browser to display them - see here for an explanation. It is quite simple to do this using the module HTML::Entities. Note also the safer 3 argument form of open()

use HTML::Entities;
open (my $fh, '>', 'tt.html') or die "Could not open tt.html, $!";
my $x= qq(<?xml version="1.0" encoding="utf-8" ?>
<Soap-ENV:Envelope>
 <Soap-ENV:Body>
  <CheckTrade>
   <tradeId>49214792</tradeId>
  </CheckTrade>
 </Soap-ENV:Body>
</Soap-ENV:Envelope>
); 
encode_entities($x);
print $fh "<table><tr><td>Message</td><td>$x</td></tr></table>";
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