Intermittent Xmas tree

Please explain its workin

The D-type flip flop transfers on the output Q the status of the signal on "D" only on positive edges of the clock; at the first instant, the first f.f. has D at 1 (see the XOR port) and obviously its Q is also set to 1 at the first positive edge of the clock.. Afterwards since the f.f. are connected in cascade and since Q of the first f.f. is to 1, also D of the second f.f. is to 1 and so its related Q is switched to 1. This process goes on until the last f.f. sets to 1 also the second input of the XOR port (moment in which all the outputs are to 1 and so all the LEDs are on) which will switch its output to 0 and propagate it to the input D of the first f.f. Now the opposite process is happening: slowly all the outputs of the f.f. are set to 0, until the last f.f. also sets its output to 0 (all outputs Q to 0 and so all the LEDs off) and the XOR port switches to 1. From here the process restarts.