Express Tree

An expression is defined as a string containing capital letters ($A$, $B$, $C$, etc.), the operators $+$, $*$, $-$ and $/$, and parentheses $($ and $)$. The operators and the parentheses follow their usual precedence rules. Given such an expression, an expression tree can be formed for the expression. Each non-leaf node of the tree is defined as follows: It has one of the operators. The children