Flatten an array using a mix of iteration and recursion

flatten.rb

def flatten(array)
  return nil unless array.is_a?(Array)
	array.each do |item|
		if item.is_a?(Array)
			flatten(item).reverse_each do |inner_item| 
				#add to array at index of item
				array.insert(array.index(item)+1, inner_item)
			end
			#remove pre-existing array
			array.delete(item)
		end
	end
end


array = ["bananas", [1,2,3], ["apple", "cheese", [100, 20]], [true], [4.0, 7, 32]]
puts flatten(array).to_s

array = ["bananas"]
puts flatten(array).to_s

array = "bananas"
puts flatten(array).to_s

array = [[["bananas"], nil]]
puts flatten(array).to_s

array = nil.to_a
puts flatten(array).to_s