The names of the keys ('fruit' and 'apple') are not numbers so it is not a matrix (array of arrays) but a set of nested objects.
Nested Array (keys are numbers):
multiArray = [[
{'berbiji' : 'ya', 'panen' : '3tahun'}]]
]]
multiArray[0][0].panen === '3tahun' // true
Nested Object (keys are strings):
multiObject = {
fruit: {
apple: {'berbiji' : 'ya', 'panen' : '3tahun'}
}
}
multiArray[group][fruit_name].panen === '3tahun' // true
Either way, the nested object or array needs to be initiated before you can assign values to keys.
To follow your example:
var multi = {}
var group = 'fruit'
var fruit_name = 'apple';
multi[group] = {} // same as multi.fruit = {}
multi[group][fruit_name] = {'berbiji' : 'ya', 'panen' : '3tahun'}
multi.fruit.apple.panen === '3tahun' // true