public Tree addElt (String element) {
	    if(element.compareTo(this.getData()) < 0){
	    	if(this.right.getData() == null){
	    		if(this.left.getData() == null)
	    			return new Tree(this.getData(), new Tree(element), true);
	    		return new Tree(this.getData(), this.left.addElt(element), true);
	    	}
	    	if(this.left.getData() == null)
	    		return new Tree(this.getData(), new Tree(element), this.right);
	    	return new Tree(this.getData(), this.left.addElt(element), this.right);
	    }
	    if(element.compareTo(this.getData()) > 0){
	    	if(this.left.getData() == null){
	    		if(this.right.getData() == null)
	    			return new Tree(this.getData(), new Tree(element), false);
	    		return new Tree(this.getData(), this.right.addElt(element), false);
	    	}
	    	if(this.right.getData() == null)
	    		return new Tree(this.getData(), this.left, new Tree(element));
	    	return new Tree(this.getData(), this.left, this.right.addElt(element));
	    }
	    return this;
	}