Tree insert(Tree t){
		if (this.op.compareTo(t.op) > 0) 
			if(this.pt == null) {
				this.pt = t;
				return this;
			} else {
				this.pt = this.pt.insert(t);
				return this;
			}
		else if(this.lt == null) {
				this.lt = t;
				return this;
			} else {
				this.lt = this.lt.insert(t);
				return this;
			}
	}