I looking for a formula to auto-assign a number based on the parent/child level.

For example, first level parent would be auto-assigned zero (0). Any sub-items would then be 1, 2, 3, etc. based on what level the item is listed under the parent. I've provided an example of how this would look, but I've manually entered in the 0,1,2,3, etc. in the 'Level assignment" column. I'm looking for a formula to replace the numbers in that column so I don't have to manually enter them when new rows and children are added to parents.

Thank you!