How to categorise xml api output by Division

I am working in Codeigniter project where i need to show vacancies category wise from api results.

I have XML output like this

<Vacancy ID="1">
    <VacancyID>1</VacancyID>
    <Division ID="1">Div 1</Division>
    // Other Data
</Vacancy>
<Vacancy ID="2">
    <VacancyID>2</VacancyID>
    <Division ID="2">Div 2</Division>
    // Other Data
</Vacancy>
<Vacancy ID="3">
    <VacancyID>3</VacancyID>
    <Division ID="1">Div 1</Division>
    // Other Data
</Vacancy>

I want to categorise vacancies by division so i want to convert this into something like

<Division ID="1">
   <Vacancy ID="1">
      <VacancyID>1</VacancyID>
      <Division ID="1">Div 1</Division>
      // Other Data
   </Vacancy>
   <Vacancy ID="3">
      <VacancyID>3</VacancyID>
      <Division ID="1">Div 1</Division>
      // Other Data
   </Vacancy>
</Division>
<Division ID="2">
   <Vacancy ID="2">
      <VacancyID>2</VacancyID>
      <Division ID="2">Div 2</Division>
      // Other Data
   </Vacancy>
</Division>

How can i achieve this?