fix the wording

modules/bintree.md

@@ -4,11 +4,13 @@ Write a program that creates a binary tree with N + 1 nodes, where N
 is specified as a command line argument.
 
 Each node, besides the root (that is always created), will contain an
-integer and will be created like this: take a binary representation of the
+integer member and will be created like this: take a binary representation of the
 number in the sequence {0, 1, ..., N - 1} and traverse the pre-existing tree
 using this representation until a `NULL` node pointer is found.  0 means the
 left child, 1 means the right one.
 
+Only the leaf nodes actually contain the number.
+
 For example, for 5 (101 in binary), the tree will be created as follows:
 
   1. create root node
@@ -20,5 +22,5 @@ Once the tree is populated, traverse the tree (choose your method), count the
 nodes and print the number to the standard output.
 
 Variant: add a function pointer to each node that will be called on its visit.
-The number stored in the node will be the sole argument of this function.i  Use
+The number stored in the node will be the sole argument of this function. Use
 that to traverse the tree and free the memory in the process.