Rewrite tree encoding

This is simpler and less error prone. Just compare right->ch and if it doesn't
match, check if next left is the last left.

tree.c

@@ -100,26 +100,14 @@ static int write_entry(struct BIT_BUFFER *bitbuf, struct tree *parent,
 		left = parent->left;
 		right = parent->right;
 
-		if (c != 0) {
-			if (left->ch == c) {
-				bit = 0;
-				bb_write(bitbuf, &bit, 1);
-				break;
-			} else if (right->ch == c) {
-				bit = 1;
-				bb_write(bitbuf, &bit, 1);
-				break;
-			}
-		} else {
-			if (left->left == NULL) {
-				bit = 0;
-				bb_write(bitbuf, &bit, 1);
-				break;
-			} else if (right->ch == c) {
-				bit = 1;
-				bb_write(bitbuf, &bit, 1);
-				break;
-			}
+		if (right->ch == c) {
+			bit = 1;
+			bb_write(bitbuf, &bit, 1);
+			break;
+		} else if (left->left == NULL) {
+			bit = 0;
+			bb_write(bitbuf, &bit, 1);
+			break;
 		}
 
 		bit = 0;