Javascript transform flat data to nested object

I am pretty new to react/ES6 and I got a strange behavior when I use reduce method to transform a flat array I receive from an API into a nested object. I was aleready familiar with map and filter but never used reduce before.

I am pretty sure that I am using it wrong but it goes like this.

I have the folowing flat dataset:

[
  {
    category:"Category1",
    subCategory:"SubCategory1",
    productType:"ProductType1",
    brand:"brand1"
  },
  {
    category:"Category1",
    subCategory:"SubCategory2",
    productType:"ProductType2",
    brand:"brand2"
  },
  {
    category:"Category1",
    subCategory:"SubCategory2",
    productType:"ProductType2",
    brand:"brand3"
  },
  {
    category:"Category2",
    subCategory:"SubCategory1",
    productType:"ProductType1",
    brand:"brand1"
  },
  {
    category:"Category2",
    subCategory:"SubCategory1",
    productType:"ProductType2",
    brand:"brand2"
  }
]

I am using the folowing code to get a nested object from the flat dataset.

getNestedData() {
  var baseData = this.getBaseData();

  return baseData.reduce((categories,category) => {
    if(!categories[category.category]){
      categories[category.category] = {
        category: category.category,
        subCategories: baseData.filter(bd => bd.category === category.category)
          .reduce((subCategories,subCategory) => {
            if(!subCategories[subCategory.subCategory]) {
              subCategories[subCategory.subCategory] = {
                subCategory: subCategory.subCategory,
                productTypes: baseData.filter(bd => bd.category === subCategory.category && bd.subCategory === subCategory.subCategory)
                  .reduce((productTypes,productType) => {
                    if(!productTypes[productType.productType]) {
                      productTypes[productType.productType] = {
                        productType: productType.productType,
                        brands: baseData.filter(bd => bd.category === productType.category && bd.subCategory === productType.subCategory && bd.productType === productType.productType)
                          .reduce((brands,brand) => {
                            if(!brands[brand.brand]) {
                              brands[brand.brand] = {
                                brand: brand.brand
                              }
                            }
                            return brands;
                          }) 
                      };
                    }
                    return productTypes;
                  })
              };
            }
            return subCategories;
          })
      }
    }
    return categories;
  });
}

However, the result isn't what I expected. It returns the root array object inside the first category of the array. Like Category1 => [Category1,Category2]. And if you go under the category1 child the same thing happen.

I prepared the following jsFiddle to show my issue.

Let me know what I am doing wrong I googled this for hours. I would also like to know if this way is the most efficient one?

Edit:

There is an example of the expected output:

[
  {
    category: "Category1"
    subCategories:[
      {
        subCategory:"SubCategory1",
        productTypes:[
          {
            productType:"ProductType1",
            brands:["Brand1"]    
          }
        ]   
      },
      {
        subCategory:"SubCategory2",
        productTypes:[
          {
            productType:"ProductType2",
            brands:["Brand2","Brand3"]
          }   
        ]
      }
    ]
  },
  {
    category: "Category2",
    subCategories:[
      {
        subCategory:"SubCategory1",
        productTypes:[
          {
            productType:"ProductType1",
            brands:["Brand1"]
          },
          {
            productType:"ProductType2",
            brands:["Brand2"]
          }
        ]
      }
    ]
  }
]

Edit

Mat was right I forgot to pass the initial value when I was using reduce. Passing the initial value made reduce work as I expected. I have then been able to change my code to get the expected result. The code isn't the most elegant but works very well:

getNestedData()
{
    var baseData = this.getBaseData();
  return baseData
  .map(c => {return c.category;})
  .reduce((categories,category) => {
  var currentCategory = categories.filter(
    c => c.category === category
  );
    if (currentCategory.length === 0) {
            var categoryData = baseData.filter(bd => bd.category === category);
      categories.push({
        category:category,
        subCategories: categoryData
        .map(c => {return c.subCategory})
        .reduce((subCategories,subCategory) => {
            var currentSubCategory = subCategories.filter(sc => sc.subCategory === subCategory)
            if(currentSubCategory.length === 0)
          {
            var subCategoryData = categoryData.filter(cd => cd.subCategory === subCategory);
            subCategories.push({
                subCategory:subCategory,
              productTypes: subCategoryData
              .map(scd => {return scd.productType})
              .reduce((productTypes,productType) => {
                var currentproductType = productTypes.filter(pt => pt.productType === productType);
                if(currentproductType.length === 0)
                {
                    var productTypeData = subCategoryData.filter(scd => scd.productType === productType)
                  productTypes.push({
                    productType:productType,
                    brands: productTypeData
                    .map(ptd => {return ptd.brand})
                    .reduce((brands,brand) => {
                        var currentBrand = brands.filter(b => b.brand === brand);
                      if(currentBrand.length === 0)
                      {
                        brands.push({brand:brand});
                      }
                      return brands;
                    },[])
                  });
                }
                return productTypes;
              },[])
            });
          }
          return subCategories;
        },[])
      });
    }
    return categories;
  },[])
}

There is the working jsFiddle with the expected behavior.