This is a Ruby tree! It shows every object from the Ruby Programming Language in a tree format.

add 

        # Set.add

(from ruby core)
---
    add(o)

---

Adds the given object to the set and returns self. Use `merge` to
add many elements at once.
    Set[1, 2].add(3)                    #=> #<Set: {1, 2, 3}>
    Set[1, 2].add([3, 4])               #=> #<Set: {1, 2, [3, 4]}>
    Set[1, 2].add(2)                    #=> #<Set: {1, 2}>

This is MURDOC! A Ruby documentation browser inspired by Smalltalk-80. It allows you to learn about Ruby by browsing through its class hierarchies, and see any of its methods.