Heres how it works...Im the breeder of the 'isan indigo'.... I gave it that name. Its one special tree that I selected from growing out multiple trees from one fruit. I selected it from an unnamed fruit from Thailand... planted seeds and ive grown them and observed them for 6 years now. There was one outstanding tree.... Its the one I called 'Isan Indigo'. Its siblings are inconsisent in production and much lower too. One sibling chewy purple tree 20 ft away only made one fruit last year and its 8 foot tall and already leafed out. The 'Isan Indigo' is just now breaking dormancy and made around 75 fruits at 8-9 ft tall.
But can you really compare one seedling tree to it's siblings? Sure it could be "the one" but replication is the hallmark of the scientific method. I wish you well with this one and most likely once you have a dozen grafted trees in production you will find they all behave exactly alike but who knows until you have replicated it in a grafted form? Maybe you already have the test going, let us know how it goes.
Yes you can compare trees to its siblings, that the best way to find an improvement in one generation... keep the best replant and cull the bad stuff so the pollen cant ruin your project....this is called 'selective breeding' thats why im calling myself a breeder but use the term loosely. define it how you will, I do this with many plants, wheter it be perennial or annuals vegetables, and fruit. our entire farm is an experimental breeding center if you want to think of it that way.
Many people think sugar apple are 'true to seed' ... when in fact they are more likely to be 'similar to parent' just like many seeds.
basically find a desriable fruit to start with, plant out seeds, compare them as they grow for many years, taste them, let them flood, go through hurricanes, experience freezing weather, whatever... etc. You then grow seed from the best one, keep doing this. Depending on what your breeding for you select based on those characteristics you want to breed. Many things to breed for including shelf life, color, texture, disease resistant, cold hardiness, the list goes on.... breeding plants can take generations and its many peoples life work.
happy growing!