Ok, you can omit noise and leave only the chromatic scale (12 notes). In this space you will have to go through all possible combinations of notes in a chord an

Ok, you can omit noise and leave only the chromatic scale (12 notes). In this space you will have to go through all possible combinations of notes in a chord and then all possible sequences of chords for some, say, 16 bars, plus you have to generate the theme on top of your chords (or the theme first and then the chords - that will do too). Then possibly variations, improvizations, and so on. Then there may be deliberate "detuned" elements, like in Gilmour's solo improvizations or Nina Simone's vocals. This looks like a huge tree for your search. To add complexity, in some modern genres like electronica musicians also express themselves using timbre dynamics combined with notes. But apart from that, there's a problem with identifying automatically which of your variants you generated are good, which comes down to what is good music. Then performance. We usually appreciate good performance and a lot of people are not interested in hearing precise robotic play. Again, what makes a performance good? Nobody knows, there's no theory. Having said that, what's the point of doing tree search at all?