Auto Outlining In Excel

I have a hiarchal list of part numbers and their relationships to each other that is flat. The first column has a number (1-9) that identifies the hierarchal level. 1 is the top 9 is the bottom. A #1 part could have many 2s and each 2 could have many threes etc. The rows are sorted so that if you have a number 2 all the 3s or higher below it are part of that 2 until you come to another 2 and then it starts over.

I want to automatically turn on Excels outline feature so that the data can be collapsed to all the 1s. or 2s etc as I desire. Since I have the first column list the levels can't excel automatically to that? See the attachment.

Thanks