Adds a leaf value to a binary path specified by path
if (path.length() == 0) {
this.value = value;
return;
}
char charAt = path.charAt(0);
BTree branch;
if (charAt == '0") {
if (zero == null)
zero = new BTree();
branch = zero;
} else {
if (one == null)
one = new BTree();
branch = one;
}
branch.addString(path.substring(1), value);