The term ‘organisation’ is often used in the context of types business organisations so in that sense a sole trader is a type of business organisation. ‘Sole trader’ means a legal structure one owner and one boss, though there can be many employees
However, the term ‘organisation’ can also be defined as: “A social arrangement which pursues collective goals, which controls its own performance, and which has a boundary separating it from its environment”.
If you are really working on your own, just you and no-one else, you would be a sole trader but, I don’t think you are part of any sort of organisation.