OAS2Tree is a tool designed to transform OpenAPI Specification (OAS) documents into tree-like visualizations, aiding in the understanding and navigation of the structure of REST APIs. By converting the detailed, verbose, and often complex OAS files into a visual tree structure, OAS2tree simplifies the comprehension of a Web API, highlighting the hierarchical relationships between endpoints, operations, and parameters. This visual representation is particularly useful for developers and stakeholders who need a quick overview of an API without delving into the intricate details of its technical specifications. OAS2tree can be integrated into the IDE through a Visual Studio code extension or used as a standalone web application. The tool currently has about 400 users and has been used on teaching, research, and development projects. In this paper, we present the design and implementation of OAS2tree, highlighting its features and use cases. We also highlight the limitations of the current version and discuss future improvements and potential extensions.