How can i get value from C1 C2
Juggling Buckets and tags can get tricky.
If you leave your Bucket as 'SACA', you can use tags like "C1/dri" or "C1/peo" to get to your data directly.
That C2, however, looks like a spinster, with no children.
How many "C" 's will there be in the complete app? You could simply return all the data for SACA, and then parse it from there...
Very often, the firebase people recommend for you to "normalise" your data, which, in plain speech, would mean posting the data in a different format, in order to make it more accessible to a query.
For example you appear to be interested in the dri and peo tags, so store these again like so:
dri
-- C1 : "Tran Quang Minh"
-- C2 : "Other value"
peo
-- C1 : 0
-- C2 : 3
then you can simply request dri or peo with the firebase blocks and get all those values.