mjhjmtu

I read the following sentence from an instruction

Process ID 0 is usually the scheduler process and is often known as the swapper. No program on disk corresponds to this process, which is part of the kernel and is known as a system process. Process ID 1 is usually the init process and is invoked by the kernel at the end of the bootstrap procedure.

Check the processes:

$ pstree -p $$ 
-+= 00001 root /sbin/launchd
 -+= 00264 me /Applications/Utilities/Terminal.app/Contents/MacOS/Terminal -psn_0_53261
 -+= 00365 root login -pfl me /bin/bash -c exec -la bash /usr/local/bin/bash
 -+= 00366 me -bash
 |-+= 06305 me pstree -p 366
 | --- 06307 root ps -axwwo user,pid,ppid,pgid,command

Could find process 1 but where is process 0?

BSD ps doesn't show PID 0:

$ ps -o pid,ppid,comm -p 0,1,$$
 PID PPID COMM
 1 0 /sbin/launchd
14705 14704 -zsh

Since pstree uses ps to get process information (as you can see in your output), obviously it can't show PID 0.

Use top, or Activity Manager, on OSX to see PID 0:

$ top -l1 -pid 0
Processes: 480 total, 2 running, 478 sleeping, 2777 threads
2018/11/15 12:20:36
Load Avg: 1.99, 2.21, 2.13
CPU usage: 6.59% user, 18.33% sys, 75.7% idle
SharedLibs: 207M resident, 50M data, 40M linkedit.
MemRegions: 135141 total, 7727M resident, 63M private, 2624M shared.
PhysMem: 16G used (6717M wired), 61M unused.
VM: 3304G vsize, 1297M framework vsize, 5481932(0) swapins, 6319905(0) swapouts.
Networks: packets: 2367177/1916M in, 1966560/789M out.
Disks: 2569936/63G read, 1879985/62G written.

PID COMMAND %CPU TIME #TH #WQ #PORTS MEM PURG CMPRS PGRP PPID STATE BOOSTS %CPU_ME %CPU_OTHRS UID FAULTS COW MSGSENT MSGRECV SYSBSD SYSMACH CSW PAGEINS IDLEW POWER INSTRS CYCLES USER #MREGS RPRVT VPRVT VSIZE KPRVT KSHRD
0 kernel_task 0.0 47:24.02 211/8 0 0 71M+ 0B 0B 0 0 running 0[0] 0.00000 0.00000 0 400853+ 0 82636075+ 75828596+ 0 0 295335075+ 0 14150823 0.0 0 0 root N/A N/A N/A N/A N/A N/A