There's this string containing B, W and G (standing for black, white and gray). It defines the pre-ordered path of the quadtree I want to build. I wrote this method for filling the QuadTree class I also wrote but it doesn't work, it inserts correctly until it reaches a point in the algorithm it needs to "return".

I use math quadrants convention order for insertion, such as northeast, northwest, southwest and southeast. A quadtree has all it's leafs black or white and all the other nodes gray

The node used in the tree is called Node4T and has a char as data and 4 references to other nodes like itself, called, respectively NE, NW, SW, SE.

public void insert(char val)
{
    if(root==null)
    {
        root = new Node4T(val);
    }
    else
    {
        insert(root, val);
    }
}

public void insert(Node4T n, char c)
{
    if(n.data=='G') // possible to insert
    {
        if(n.NE==null)
        {
            n.NE = new Node4T(c);
            return;
        }
        else
        {
            insert(n.NE,c);
        }
        if(n.NW==null)
        {
            n.NW = new Node4T(c);
            return;
        }
        else
        {
            insert(n.NW,c);
        }
        if(n.SW==null)
        {
            n.SW = new Node4T(c);
            return;
        }
        else
        {
            insert(n.SW,c);
        }
        if(n.SE==null)
        {
            n.SE = new Node4T(c);
            return;
        }
        else
        {
            insert(n.SE,c);
        }
    }
    else // impossible to insert
    {

    }
}

The input "GWGGWBWBGBWBWGWBWBWGGWBWBWGWBWBGBWBWGWWWB" is given a char at a time to the insert method and then the print method is called, pre-ordered, and the result is "GWGGWBWBWBWGWBWBW".

How do I make it import the string correctly? Ignore the string reading process, suppose the method is called and it has to do it's job.