Bernie Sanders was treated the same as many other candidates. He wasn't a favorite of the party, and they surely tried to get Clinton nominated. However, he wasn't treated badly, just that he wasn't the favorite. He put up a good fight, but in the end didn't have what it took to beat Hillary Clinton.
Bernie Sanders was mistreated during the primary election. This was evidenced during the event of the primary election. It was also all over the internet. I believe this was not the right thing to do. Even if Bernie Sanders vowed not to support the democratic, she did not deserve this.
While it is one thing for members of a party's establishment to have favorites, the treatment of Bernie Sanders by a number of Democratic officials was deplorable and betrayed the ideals of a free society. Polling data and other resources were denied to the Sanders campaign, while senior officials made no qualms about the fact that they were actively working against a Sanders candidacy.
Even assuming that Sanders was somewhat mistreated during the Democratic primaries, he still had no shot to win. I understand Bernie supporters being angry, but at the end of the day, the Dems had to try to support the most viable candidate. Even though that clearly failed, I don't blame the party for making that choice.