Tree testing is a way to evaluate the structure of your website or application, along with card sorting (and is basically a reverse variety of this study) – these two research methods are complementing each other and can provide a better understanding of how the users navigate within your service architecture.
In this kind of study users are asked to complete a specific task and indicate the needed category location in the “tree” – hierarchical category structure of the website or app. Tree testing provides some insights from the customers that can give you a better understanding of the effectiveness of your product’s navigation hierarchy.
Tree testing was pioneered by Donna Spencer in the 2000's and was performed with paper index cards back then. Nowadays, researchers can also use some online digital tools to conduct this kind of study.
You may use tree testing as a follow-up to the card sorting research. It will allow you to evaluate and compare the user-expected website structure and your current product architecture. This approach can be helpful in the advance of designing final page layouts and could let you explore how the menu categories should work.
Tree testing is a great opportunity to enhance your product architecture and check if the structure of your product lets the users complete their goals.