XSLT Recursive function (Parent - child relationship)

I have trouble finding a solution for the following problem:

I need to give a property with the XSLT that is equal to a:CrsNr. Now it has to find the right node where the input property matches a:CrsNr. After the right node is found it needs to print all the definitions from the upper levels from high to low seperated by ::.

The nodes are linked by Code and ParentCode

I'll give you a XML and output example

XML

<a:OrganisatieEenheid>
  <a:Code>00000001</a:Code>
  <a:Level>0</a:Level>
  <a:Definition>Antwerpen</a:Definition>
  <a:CrsNr>7001</a:CrsNr>
  <a:ParentCode i:nil="true"/>
</a:OrganisatieEenheid>
<a:OrganisatieEenheid>
  <a:Code>00000004</a:Code>
  <a:Level>1</a:Level>
  <a:Definition>Zorgbedrijf</a:Definition>
  <a:CrsNr>7004</a:CrsNr>
  <a:ParentCode>00000001</a:ParentCode>
</a:OrganisatieEenheid>
<a:OrganisatieEenheid>
  <a:Code>00000426</a:Code>
  <a:Level>2</a:Level>
  <a:Definition>Raad van Beheer</a:Definition>
  <a:CrsNr>7426</a:CrsNr>
  <a:ParentCode>00000004</a:ParentCode>
</a:OrganisatieEenheid>

output

<output>
   <Definition>Antwerpen::Zorgbedrijf::Raad van Beheer</Definition>
   <InputCrs>7426</InputCrs>
</output>