Double listing concept has some rules, to follow that instruction. Now you are thing about what is Double listing? & why I do it? So answer is here!
Sometimes Google shows two page result of one site in Google search this is called as a double listing or Indented listing. This is process to get equal link rank in top 10 result but need two pages very relevant content. This is totally depend on the strength of your domain/site and the competition of your site, it goes to for double listings for long tail phrases which already bring traffic to your site from one article. It’s easy to achieve, and improves traffic because in top ten 2 results is your website in SERPS.

The way to get To get a double or indented listing process explain by Aaron Wall:
1. A bit of Domain Authority
2. Targeted, relevant articles
3. Internal Linking (esp. between articles)
4. The odd link from external sites (if any)
i.e. nothing spectacular. It’s quite simple stuff.