python xml version missing

i am using python xml to update some xml date i have small problem ,when i update the xml it cant write xml version this is my code

import xml.etree.ElementTree as ET
tree = ET.parse(r'c:\users\g\desktop\IT_ADMINVersionTrack.xml')
root = tree.getroot()

for country in root.findall('dtModule'):
  f = country.find('FolderName').text
  print "FOLDER:",f
  v = country.find('Version').text
  print "OLD VERSION:",v
  if v == "11.0":        
    country.find('Version').text = "12.0"
    v2 = country.find('Version').text
    print "NEW VERSION",v2
  else:        
    print "NO CHANGE IN VERSION"

  tree.write(r'c:\users\g\desktop\output.xml')

input xml:

<?xml version="1.0"?>
output xml:
<dsModule>
<dtModule>
<ModuleName>IT_ADMIN</ModuleName>
<Version>11.0</Version>
<FolderName>IT_ADMIN\ItDataCompInterface.dll.gz</FolderName>
<Type>P</Type>
<ClientId />
<Destination />
</dtModule>
</dsModule>

output xml:

<dsModule>
<dtModule>
<ModuleName>IT_ADMIN</ModuleName>
<Version>12.0</Version>
<FolderName>IT_ADMIN\ItDataCompInterface.dll.gz</FolderName>
<Type>P</Type>
<ClientId />
<Destination />
</dtModule>
</dsModule>

xml version is missing