title: Expand single row into multiple rows if next column has content in a spreadsheet
body: <p>I have a tree structure defined in a Google spreadsheet. I need to modify the following structure:</p>
  
  <pre><code>+---+------------+-----------------+--------------------+-----+--------------+
  |   |     A      |        B        |         C          |  D  |      E       |
  +---+------------+-----------------+--------------------+-----+--------------+
  | 1 | Techniques | Adduction d'eau | Conduites en fonte | Eau | Tuyaux       |
  | 2 |            |                 |                    |     | Robinetterie |
  | 3 |            |                 |                    |     | Outils       |
  | 4 |            |                 |                    |     | Accessoires  |
  | 5 |            |                 |                    | Gaz | Tuyaux       |
  | 6 |            |                 |                    |     | Robinetterie |
  | 7 |            |                 |                    |     | Outils       |
  | 8 |            |                 |                    |     | Accessoires  |
  +---+------------+-----------------+--------------------+-----+--------------+
  </code></pre>
  
  <p>into this:</p>
  
  <pre><code>+----+------------+-----------------+---------------------+-----+--------------+
  |    |     A      |        B        |          C          |  D  |      E       |
  +----+------------+-----------------+---------------------+-----+--------------+
  |  1 | Techniques |                 |                     |     |              |
  |  2 |            | Adduction d'eau |                     |     |              |
  |  3 |            |                 | Conduites en fonte  |     |              |
  |  4 |            |                 |                     | Eau |              |
  |  5 |            |                 |                     |     | Tuyaux       |
  |  6 |            |                 |                     |     | Robinetterie |
  |  7 |            |                 |                     |     | Outils       |
  |  8 |            |                 |                     |     | Accessoires  |
  |  9 |            |                 |                     | Gaz |              |
  | 10 |            |                 |                     |     | Tuyaux       |
  | 11 |            |                 |                     |     | Robinetterie |
  | 12 |            |                 |                     |     | Outils       |
  | 13 |            |                 |                     |     | Accessoires  |
  +----+------------+-----------------+---------------------+-----+--------------+
  </code></pre>
  
  <p>Any idea how to proceed? Thanks in advance</p>