Declaring object onto the stack in class definition vs in constructor

When I declare the "Level" object in the "LevelEditor" class definition like so, everything works fine:

class LevelEditor
{
public:
    LevelEditor(int w, int h, Shader* shader)
    {
        width = w;
        height = h;
        for (int y = 0; y < height; y++)
        {
            for (int x = 0; x < width; x++)
            {
                tile[x][y] = new WorldSprite(tileWidth * x, tileHeight * y, tileWidth, tileHeight, shader);
            }
        }
    }

    //...
private:

    //...
    Level level = Level(50, 50);

    WorldSprite* tile[300][300];

    //tile characteristics
    int tileWidth = 50;
    int tileHeight = 50;

    //flags
    bool editing = true;
};

But when I declare the "Level" object in the "LevelEditor" constructor like so, I get a stack overflow:

class LevelEditor
{
public:
    LevelEditor(int w, int h, Shader* shader)
    {
        width = w;
        height = h;
        for (int y = 0; y < height; y++)
        {
            for (int x = 0; x < width; x++)
            {
                tile[x][y] = new WorldSprite(tileWidth * x, tileHeight * y, tileWidth, tileHeight, shader);
            }
        }
        //NOTE: width and height both equal 50
        level = Level(width, height);
    }

    //...
private:

    //...
    Level level;

    WorldSprite* tile[300][300];

    //tile characteristics
    int tileWidth = 50;
    int tileHeight = 50;

    //flags
    bool editing = true;
};

This makes me wonder what the difference is between declaring a variable in the class definition and in the constructor is besides the fact of the time of defining the variable. Any idea of what the cause could be? and how I could declare the "Level" object in the constructor without having to put anything on the heap?