a simple parent symbol Xena needed sending that with my n minus 1 symbols now this M resembled x and y the extra cost will be px plus py y is down the number of times you have to go down that extra level in a tree to reach x and y is P of X plus P of y if you only have to go to the parent of x + y you wouldn't have to go that extra level and whenever you have to go to extra level it cost you one extra bit it happens P of X plus P of y fraction of the time now the end symbol Huffman code tree adds this minimal cost to the