swift – URLSession shared – memory leak

I have a scheduled timer requesting a url every x seconds. For some reason URLSession.shared fills the memory slowly over time and never frees it. Anyone an idea why this is happening?

import Foundation

DispatchQueue.global(qos: .default).async {
    let url = URL(string: "https://upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Italian_States-Piacenza_1626_2_Doppie.jpg/2880px-Italian_States-Piacenza_1626_2_Doppie.jpg")!
    Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { timer in
        URLSession.shared.dataTask(with: url) { _, _, _ in