European tree frog – Hyla arborea
is a small tree frog found in Europe, Asia and part of Africa. Based on molecular genetic and other data, a number of taxa formerly treated as subspecies of H. arborea are now generally recognized as full species.

European tree frogs are small; males range from 32–43 mm (1.3–1.7 in) in length, and females range from 40–50 mm (1.6–2.0 in) in length. They are slender, with long legs. Their dorsal skin is smooth, while their ventral skin is granular. Their dorsal skin can be green, gray, or tan depending on the temperature, humidity, or their mood. Their ventral skin is a whitish color, and the dorsal and ventral skin is separated by a dark brown lateral stripe from the eyes to the groin. Females have white throats, while males have golden brown throats with large (folded) vocal sacs. The head of H. arborea is rounded, the lip drops strongly, the pupil has the shape of a horizontal ellipse, and the tympanum is clearly recognizable. The discs on the frog’s toes, which it uses to climb trees and hedges, is a characteristic feature of H. arborea . Like other frogs, their hind legs are much larger and stronger than the fore legs, enabling the frogs to jump rapidly.

It sounds like this
Recording by Hazevoet, Cornelius J.