Parent child relationship(excel) capture the parent tree structures

What is the correct formula to always capture the parent item which is dictated by the level in column B?

Currently using this excel formula but doesn't work when there is more than 1 level 5 item for each level 4 parent item. The formula is pasted in the parent column.

=IF(B29=4,"",IF(B29=5,C28)).

Basically it works up until the last two values. The last 2 values GD00459192, GD00471958 should be GD00471889 because that is the level 4 parent just like a normal levelled tree structure of parent child relationship.


As aside this spreadsheet can be 1 big 'levelled' tree structure with multiple levels the task is to identify the ' parent item each time.

Does anyone know the whole formula for multiple levels?


Imagine a list of parts to make/manufacture a car and you want to know where each item is used i.e what the parent item is. This is what I am trying to achieve.


Thanks folks