create left son of root
public void set_Left ( String key , int root ) { int t = ( root * 2 ) + 1 ; if ( str [ root ] == null ) { Console . Write ( " Can ' t ▁ set ▁ child ▁ at ▁ { 0 } , ▁ no ▁ parent ▁ found STRNEWLINE " , t ) ; } else { str [ t ] = key ; } }