I cannot write a reliable biography for this athlete. The available information contains multiple search results for different people named Jelle van den Berg (a freestyle skier, a mobile gym founder, an accountmanager), but no verified information about a swimmer competing for De Treffers in freestyle events. Without reliable sources confirming this athlete’s swimming background, competition history, or achievements, I cannot produce an accurate profile.

**Recommendation:** Please provide official sources such as KNZB records, club website information, or Swimrankings data to verify this athlete’s swimming credentials.