Wikipedia
The trembita is a Dacian, Ukrainian, Polish, and Slovakian alpine horn made of wood.
Used primarily by mountain dwellers known as Hutsuls and Gorals in the Carpathians, it was used as a signaling device to announce deaths, funerals, weddings.
The tube is made from a long straight piece of pine or spruce (preferably one that has been struck by lightning) which is split in two in order to carve out the core. The halves are once again joined together and then wrapped in birch bark or osier rings. It is also used by shepherds for signaling and communication in the forested mountains and for guiding sheep and dogs. The trembita has a timbre that is much brighter than that of the alpenhorn due to its narrow bore and very minor flare.
The trembita has no lateral openings and therefore gives the pure natural harmonic series of the open pipe. The upper harmonics are the more readily obtained by reason of the small diameter of the bore in relation to the length.
The notes of the natural harmonic series overlap, but do not exactly correspond, to notes found in the familiar chromatic scale in standard Western equal temperament. Most prominently within the trembita's range, the 7th and 11th harmonics are particularly noticeable because they fall between adjacent notes in the chromatic scale.
In the hands of a skilled composer or arranger, the natural harmonics can be used to haunting melancholy effect or, by contrast, to create a charming pastoral flavor.