This is not how TileMaps work. A TileSet is a resource that contains only a limited amount of information per tile: texture, collision shape, navigation shape, and/or occlusion shape.
Don't let the fact that you can use nodes as helpers to make a TileSet lead you to think of them as individual nodes. When using the TileMap, it is one object with a single texture (made up of all the tile textures added together), one collision shape (the combination of the individual tiles' shapes), etc.
When you collide, you're colliding with the TIleMap. Using the location of that collision, you can tell what type of tile you're on.