error: ambiguous use of inherited type

ambiguous.swift

class A {
	enum Reusable {
		case option1
	}
}

class B: A {
	enum Reusable {
		case option1
	}
	
	func process() {
		_ = B.Reusable.option1
		
		//		Untitled.swift:13:9: error: ambiguous use of 'option1'
		//				_ = B.Reusable.option1 // how this is ambiguous?
		//				      ^
		//		Untitled.swift:9:8: note: found this candidate
		//				case option1
		//				     ^
		//		Untitled.swift:3:8: note: found this candidate
		//				case option1
		//				     ^
		
	}
}

let a = A()
let b = B()