You'd be much better off using a tool like xidel that can manipulate csv / raw text and understands JSON:

I'm going to assume so_24300508.csv :

(this is extracted from your JSON sample instead of the CSV sample you provided)

xidel -s so_24300508.csv --json-mode=deprecated --xquery '
  [
    let $csv:=x:lines($raw)
    for $region in distinct-values($csv ! tokenize(.,",")[1])
    return {
      "name":$region,
      "children":[
        for $country in distinct-values($csv[starts-with(.,$region)] ! tokenize(.,",")[2]) return {
          "name":$country,
          "children":for $data in $csv[starts-with(.,$region) and contains(.,$country)]
          let $value:=tokenize($data,",")
          return {
            "name":$value[3],
            "size":$value[4]
          }
        }
      ]
    }
  ]
'

(without --json-mode=deprecated replace [ ] with array{ })

See this code snippet for intermediate steps leading to this query.
Also see this online xidelcgi demo.

Output:

[
  {
    "name": "Africa",
    "children": [
      {
        "name": "Kenya",
        "children": [
          {
            "name": "NAI",
            "size": "109"
          },
          {
            "name": "NAA",
            "size": "160"
          }
        ]
      }
    ]
  },
  {
    "name": "Asia",
    "children": [
      {
        "name": "India",
        "children": [
          {
            "name": "NSI",
            "size": "100"
          },
          {
            "name": "BSE",
            "size": "60"
          }
        ]
      },
      {
        "name": "Pakistan",
        "children": [
          {
            "name": "ISE",
            "size": "120"
          },
          {
            "name": "ANO",
            "size": "433"
          }
        ]
      }
    ]
  },
  {
    "name": "European Union",
    "children": [
      {
        "name": "United Kingdom",
        "children": [
          {
            "name": "LSE",
            "size": "550"
          },
          {
            "name": "PLU",
            "size": "123"
          }
        ]
      }
    ]
  }
]

Please don't use RegEx, or Bash' builtin tools. They're not designed to parse or create JSON. Use a dedicated parser like xidel instead:

Assuming 'input.csv':

$ xidel -s "input.csv" -e '
  array{
    let $csv:=x:lines($raw) ! array{tokenize(.,",")}
    for $region in distinct-values($csv(1))
    return {
      "name":$region,
      "children":array{
        for $country in distinct-values($csv[.() = $region](2))
        return {
          "name":$country,
          "children":array{
            $csv[.() = ($country)] ! {
              "name":.(3),
              "size":.(4)
            }
          }
        }
      }
    }
  }
'
[
  {
    "name": "Africa",
    "children": [
      {
        "name": "Kenya",
        "children": [
          {
            "name": "NAI",
            "size": "109"
          },
          {
            "name": "NAA",
            "size": "160"
          }
        ]
      }
    ]
  },
  {
    "name": "Asia",
    "children": [
      {
        "name": "India",
        "children": [
          {
            "name": "NSI",
            "size": "100"
          },
          {
            "name": "BSE",
            "size": "60"
          }
        ]
      },
      {
        "name": "Pakistan",
        "children": [
          {
            "name": "ISE",
            "size": "120"
          },
          {
            "name": "ANO",
            "size": "433"
          }
        ]
      }
    ]
  },
  {
    "name": "European Union",
    "children": [
      {
        "name": "United Kingdom",
        "children": [
          {
            "name": "LSE",
            "size": "550"
          },
          {
            "name": "PLU",
            "size": "123"
          }
        ]
      }
    ]
  }
]

See this gist for intermediate steps leading to this query.
Also see this online xidelcgi demo.