I live in Denmark, Europe and was going for a walk on a beautiful cemetary in the city. I saw this tree and would like to know what species it is.
Unfortunately i have no photos of the tree from a closer distance.
This is very likely some species of willow tree (genus Salix).
Without a better photo it will be difficult to ID this to species. To complicate matters, willows are very cross-compatible, and numerous hybrids occur, both naturally and in cultivation.
Since it appears your picture is from a garden or park, a fair guess would be the common ornamental tree:
Weeping willow (commonly Salix × sepulcralis)