Test 1

gr-0/0/0 {
        description "GRE Tunnel to Some Other device";
        unit 0 {
            tunnel {
                source x.x.x.x;
                destination y.y.y.y;
            }
            family inet {
                address 1.1.1.2/28;
            }
        }
    }
  



gr-0/0/1 {
        description "GRE Tunnel to Test2";
        unit 0 {
            tunnel {
                source a.a.a.a;
                destination b.b.b.b;
            }
            family inet {
                address 1.2.2.1/28;
            }
        }
    }

Test 2

(This Tuunnel points to Test1 - gr-0/0/1)

    gr-0/0/0 {
        description "GRE Tunnel interface to Test 1";
        unit 0 {
            tunnel {
                source b.b.b.b;
                destination a.a.a.a;
            }
            family inet {
                address 1.2.2.2/28;
            }
        }
    }