Append Elements to Expanding List : <p>I want to generate an expanding nested list. How do I generate a nested list as such?</p>

<pre><code>[1.0, None]
[-1.0, [1.0, None]]
[-1.0, [1.0, [3.0, None]]]
[6,[-1.0, [1.0, [3.0, None]]]]
</code></pre>

<p>Essentially, I want to create a nested list in which each element gets inserted into the original list. </p>
