• index of value value in tree = i
• the element at index i of stack tree = node (value, left, (-1))
• the element at index left of stack tree = node (lvalue, lleft, lright)
• find parent index of tree = p
• the element at index p of stack tree = node (pval, pleft, i)

then pop value from tree tree = result of storing (node (value, (-1), (-1))) at index i of stack (result of storing (node (pval, pleft, left)) at index p of stack tree)