@Override public String toString(String pad,int recursionLevel){
  StringBuffer result=new StringBuffer();
  result.append(pad);
  result.append("+ ROOT\n");
  for (  FPTreeNode node : m_children.values()) {
    result.append(node.toString(pad + "|  ",recursionLevel));
  }
  return result.toString();
}

@ Override public String toString ( String pad , int recursionLevel ) { StringBuffer result = new StringBuffer ( ) ; result . append ( pad ) ; result . append ( "+ ROOT\n" ) ; for ( FPTreeNode node : m_children . values ( ) ) { result . append ( node . toString ( pad + "|  " , recursionLevel ) ) ; } return result . toString ( ) ; }
get a textual description of the tree at a given recursion ( projection ) level .
