The base is original from the producer (chords and melodies), but is complemented with elements that complement the song that come from samplepacks, usually, vocal chops, guitars, wobbles sections, glitch effects. It is the standard in which most of producers work, in a project you will find MIDI files made by the producer, but also melodic loops.
Bass made with serum and used plugins ,fabfilter Q3 ,L2 , lfotool, supercharge gt.
Sample pack Mainroom melodic house & house
Loop name ff_mmht_128_piano_loop_ninetyskeys_Gmin