Concatenate data from multiple xls files

Hi, It's not really an issue anymore because I found a solution but I have the feeling that he should be much easier or intuitive. The goal: read multiple excel files and concatenate the data from these files. Some of these xls files have an extra-column information (e.g. most xls have columns A, B and C, some have columns A, B, C and D).

This can be adressed with multiple xls reader nodes and several concatenate nodes.

But since I have a large number of xls files, I would like to use the xls reader in a loop but neither the simple loop end nor the "add column" one are able to concatenate the readed xls due to inconsistency in the number of columns. So how to do it ? I found a workaround by using a transpose node before and after the loop end node (see snapshot below) but is there a better way to solve this ?