There is only one file type that uses the .TRES extension:
Godot Engine Text Resource File
A TRES file is a resource file created by Godot Engine, a free and open source game engine used to create 2D and 3D games. It contains data in plain text that is referenced by Godot Engine nodes to perform various functions in the games, such as simulating physics, setting user interfaces, and drawing sprites. TRES files can be opened and edited using the Inspector included with Godot Engine.
TRES files are saved in plain text, which allows developers to more easily control resource versions. When a developer exports the game, Godot Engine converts the TRES files to RES binary files to reduce their size and increase efficiency.
Updated: November 23, 2019