.tmux.conf

set -s escape-time 0
set -g base-index 1
set-window-option -g mode-keys vi
bind-key -t vi-copy 'v' begin-selection
bind-key -t vi-copy 'y' copy-selection
set -g history-limit 30000

set-option -g default-command "reattach-to-user-namespace -l bash"
bind C-c run "tmux save-buffer - | reattach-to-user-namespace pbcopy"
bind C-v run "reattach-to-user-namespace pbpaste | tmux load-buffer - && tmux paste-buffer"
setw -g mode-mouse on
set -g mouse-resize-pane on
set -g mouse-select-pane on
set -g mouse-select-window on

I have a slightly different setting:

set -g mode-mouse on
set-window-option -g mode-mouse on
set -g terminal-overrides 'xterm*:smcup@:rmcup@'

@burningTyger 's config worked for me