Create a button on Quote 'Populate Root Id', must work for Classic and Lightning both
Create a field on QuoteLine "Root Id" Lookup (QuoteLine)
On click of this Button we need to populate the Parent bundle Id (Parent Quote Line Item) on every child Lines
Input to your Class will be QuoteId from Quote Detail page.
NOTE: You need to identify fields at QuoteLine level where you can have immediate Parent QuoteLine Id and Bundle Product
 
For Example :
Quote Q-00001 :
QuoteLines:

• QL-00001 (Product A)
• QL-00002 (Product B)
• QL-00003 (Product C)
• QL-00004 (Product D)
• QL-00005 (Product E)
• QL-00006 (Product F)
• QL-00007 (Product G)
• QL-00008 (Product H)
• QL-00009 (Product I)
• QL-00010 (Product H)
• QL-00011 (Product J)
• QL-00012 (Product K)
• QL-00012 (Product L)
• QL-00013 (Product M)
• QL-00014 (Product N)
• QL-00015 (Product O)
• QL-00016 (Product P)
• QL-00016 (Product Q)
• QL-00001 (Product C)

Output: Highlighted in Green
Quote Q-00001 :
QuoteLines:
QL-00001 (Product A) [ROOT_ID : Null]
QL-00002 (Product B) [ROOT_ID : QL-00001]
QL-00003 (Product C) [ROOT_ID : QL-00001]
QL-00004 (Product D) [ROOT_ID : QL-00001]
QL-00005 (Product E) [ROOT_ID : QL-00001]
QL-00006 (Product F) [ROOT_ID : QL-00001]
QL-00007 (Product G) [ROOT_ID : QL-00001]
QL-00008 (Product H) [ROOT_ID : QL-00001]
QL-00009 (Product I) [ROOT_ID : QL-00001]
QL-00010 (Product H) [ROOT_ID : QL-00001]
QL-00011 (Product J) [ROOT_ID : QL-00001]
QL-00012 (Product K) [ROOT_ID : QL-00001]
QL-00012 (Product L) [ROOT_ID : QL-00001]
QL-00013 (Product M) [ROOT_ID : NULL]
QL-00014 (Product N) [ROOT_ID : QL-00013]
QL-00015 (Product O) [ROOT_ID : QL-00013]
QL-00016 (Product P) [ROOT_ID : QL-00013]
QL-00016 (Product Q) [ROOT_ID : QL-00013]
QL-00001 (Product C) [ROOT_ID : QL-NULL]

Please help me i am new apex code
Thank You