SQL & PL/SQL :: Dynamic Column Value Query?

I have a Strange requirement from client data is loaded from excel to Oracle Table- TST_TBL (with Header in Excel)

CREATE TABLE TST_TBL
(
JOB_DETAIL_ID NUMBER,
SHEET_NAME VARCHAR2(100 BYTE),
COL1 VARCHAR2(400 BYTE),
COL2 VARCHAR2(400 BYTE),
COL3 VARCHAR2(400 BYTE),
COL4 VARCHAR2(400 BYTE),

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After the Data is loaded, we see data look like the above.

(1) Always COL3 column name have data value as 'Gen1' which is the indication for us from where data starts. But Gen1, Gen2, Gen3 etc... is dynamic. ie. This month we get gen1 and gen2 columns followed by null value in a column. Next month we get gen1,2,3,4 followed by null column.
(2) Null Column indicate us that there is a break in the column.
(3) Then next we need to look for next group of data (Monthly) and then insert into the same table again with different sheet_name column.
(4) Next for Quater and then YTD. None of the column Values are fixed and its all dynamic.

If you load the below data, you will come to know what i am looking for. I tried using UNPIVOT. But couldnt able to achieve it. Is there an option to do it in sigle query? or Do I need to go for Stored Procedure?

Insert into TST_TBL
(JOB_DETAIL_ID, SHEET_NAME, COL1, COL2, COL3,
COL4)
Values
(100, 'Wire_1', 'Gen1',
'Gen2', 'Gen3', 'Gen4');
Insert into TST_TBL

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