Does the block reward comes from a bitcoin treasury? If yes, then how is it issued? The miner adds the relevant block reward to himself (i.e. 12.5 bitcoin as of now) in something called the coinbase transaction.

Where do these 12.5 bitcoins come from? Does it comes from bitcoin treasury? If yes, then how is it issued? 

Could I get a less-technical and self explanatory answer please? 



Note that my question is not sufficiently answered on Where does the money I get from mining bitcoin come from? which was suggested as a potential duplicate.
There is no treasury. The Bitcoin is generated out of nothing. The coinbase transaction has special rules. It is allowed to have only one input which has no previous output and really no value. It is allowed to create outputs which have a total value of the block subsidy (currently 12.5 BTC) plus the transaction fees from that block. Those coins aren't issued by any entity; the miner just creates the output(s) and is allowed to do so. This rule is enforced by all of the full nodes on the network who will reject that miner's block if he pays himself too much money.

Simply put, the miner is allowed to just pay himself money that is produced out of nothing.