tree, awk, sort and tr

DATA="/home/nine/lab"
SampleName="MM20567"
Folder="$DATA/merged_fastqs"
tree "$Folder"
/home/nine/lab/merged_fastqs
└── MM20567
    ├── MM20567_01_S17_L001_I1_001.fastq.gz
    ├── MM20567_01_S17_L001_R1_001.fastq.gz
    ├── MM20567_01_S17_L001_R2_001.fastq.gz
    ├── MM20567_02_S18_L001_I1_001.fastq.gz
    ├── MM20567_02_S18_L001_R1_001.fastq.gz
    ├── MM20567_02_S18_L001_R2_001.fastq.gz
    ├── MM20567_03_S19_L001_I1_001.fastq.gz
    ├── MM20567_03_S19_L001_R1_001.fastq.gz
    ├── MM20567_03_S19_L001_R2_001.fastq.gz
    ├── MM20567_04_S20_L001_I1_001.fastq.gz
    ├── MM20567_04_S20_L001_R1_001.fastq.gz
    └── MM20567_04_S20_L001_R2_001.fastq.gz

DATA="/home/nine/lab"
SampleName="MM20567"
Folder="$DATA/merged_fastqs"
cd "$Folder"
for i in $(ls -d */)
do
  SampleName="${i%%/}"
  Merged_SampleName=`echo $( ls "$SampleName" | awk -F "_" '{ print $1 "_"  $2 }' | sort -u) | tr ' ' ','`
  echo "$SampleName"
  echo "$Merged_SampleName"
done

MM20567
MM20567_01,MM20567_02,MM20567_03,MM20567_04